Astronomy

Is there a term to describe all stars that are not neutron stars or white dwarfs?

Is there a term to describe all stars that are not neutron stars or white dwarfs?


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I am looking for a official term that describes all stars that are not neutron stars or white dwarfs. "Still burning stuff stars" or "ordinary stars" are all I have been able to come up with. Is there an official term for stars that are still evolving and haven't "died" yet?


It is tempting to think that non-degenerate stars covers it, since even the structure of the lowest mass main sequence stars are not significantly affected by fermion degeneracy. Unfortunately the cores of more advanced evolutionary stages can become degenerate.

So I would go with nuclear-burning stars, although this in turn excludes pre main sequence stars.

In some ways it is easier to say a star that is not a compact stellar remnant.


Every so often someone will note that a "star" is a ball of plasma that is supported by nuclear reactions at its core, and so technically neutron stars and white dwarfs are stellar remnants, and not stars.

The technical term is therefore "star". And if you think that could be ambiguous then just spell it out: "Stars with supported by fusion reactions"/"Stars, excluding stellar remnants"


My advice would be to not seek a definition that is "official," because official definitions will often not serve the application you have in mind. Just say what you want to say, tailored to that application. We'd like definitions to be instructions for sorting everything that is from everything that isn't, but in practice they actually can't work that way. For example, what is the official definition of a "computer", that works in any context? At one level, the definition of a star should include whatever objects people who regard themselves as "stellar astronomers" study, because it is the commonality among all such stars that unites them. But most "official" definitions of a "star" already exclude many of the objects that "stellar astronomers" study! (The same holds for "planets.") So although official definitions do exist, they are often not what you want in your application. That's why I say, just define what you mean yourself, and don't even try to be "official." For example, if your interest is in stellar evolution, and you are not interested in endpoints because they are not still evolving, then say stars that are still evolving. If your interest is stars that obey an ideal gas law, you might favor a term like "ordinarily gaseous stars," or some such thing. Tailoring to the interest gives a better definition than something "official."


Q and A of the Day: White Dwarfs vs. Neutron Stars?

Q:
What are five differences between white dwarfs and neutron stars?

A:
The major difference is due to the way in which they are formed.
1. White dwarfs are formed from the collapse of low mass stars, less than about 10 time the mass of the Sun. This star loses most of its mass in a wind, leaving behind a core that is less than 1.44 solar mass. On the other hand, neutron stars are formed in the catastrophic collapse of the core of a massive star.
Other differences follow:

2. A white dwarf is supported by electron degeneracy pressure, a neutron star by neutron degeneracy pressure (go look those terms up for a quick physics lesson).
3. A white dwarf has a larger radius --about 600 times
4. A neutron star has a stronger gravitational field -about 400,000 times
5. Finally, neutron stars have higher temperatures at birth, spin faster, and have stronger magnetic fields, among other things.

Store these nuggets away for the next time you’re on Jeopardy!, or perhaps the – wait for the pun – star at your local pub's trivia night.


White dwarfs crashing into Neutron Stars explain loneliest supernovae

A research team led by astronomers and astrophysicists at the University of Warwick have found that some of the Universe’s loneliest supernovae are likely created by the collisions of white dwarf stars into neutron stars.

Dr Joseph Lyman from the University of Warwick is the lead researcher on the paper, The progenitors of calcium-rich transients are not formed in situ, published today by the journal Monthly Notices of the Royal Astronomical Society (and can be read here).

“Our paper examines so-called `calcium-rich' transients” says Dr Lyman. “These are luminous explosions that last on the timescales of weeks, however, they're not as bright and don't last as long as traditional supernovae, which makes them difficult to discover and study in detail”.

Previous studies had shown that calcium comprised up to half of the material thrown off in such explosions compared to only a tiny fraction in normal supernovae. This means that these curious events may actually be the dominant producers of calcium in our universe.

“One of the weirdest aspects is that they seem to explode in unusual places. For example, if you look at a galaxy, you expect any explosions to roughly be in line with the underlying light you see from that galaxy, since that is where the stars are” comments Dr Lyman. “However, a large fraction of these are exploding at huge distances from their galaxies, where the number of stellar systems is miniscule.

“What we address in the paper is whether there are any systems underneath where these transients have exploded, for example there could be very faint dwarf galaxies there, explaining the weird locations. We present observations, going just about as faint as you can go, to show there is in fact nothing at the location of these transients - so the question becomes, how did they get there?”

Calcium-rich transients observed to date can be seen tens of thousands of parsecs away from any potential host galaxy, with a third of these events at least 65 thousand light years from a potential host galaxy.

The researchers used the Very Large Telescope in Chile and Hubble Space Telescope observations of the nearest examples of these calcium rich transients to attempt to detect anything left behind or in the surrounding area of the explosion.

The deep observations taken allowed them to rule out the presence of faint dwarf galaxies or globular star clusters at the locations of these nearest examples. Furthermore, an explanation for core-collapse supernovae, which calcium-rich transients resemble, although fainter, is the collapse of a massive star in a binary system where material is stripped from the massive star undergoing collapse. The researchers found no evidence for a surviving binary companion or other massive stars in the vicinity, allowing them to reject massive stars as the progenitors of calcium rich transients.

Professor Andrew Levan from the University of Warwick’s Department of Physics and a researcher on the paper said:

“It was increasingly looking like hypervelocity massive stars could not explain the locations of these supernovae. They must be lower mass longer lived stars, but still in some sort of binary systems as there is no known way that a single low mass star can go supernova by itself, or create an event that would look like a supernova.”

The researchers then compared their data to what is known about short-duration gamma ray bursts (SGRBs). These are also often seen to explode in remote locations with no coincident galaxy detected. SGRBs are understood to occur when two neutron stars collide, or when a neutron star merges with a black hole – this has been backed up by the detection of a 'kilonova' accompanying a SGRB thanks to work led by Professor Nial Tanvir, a collaborator on this study. Although neutron star and black hole mergers would not explain these brighter calcium rich transients, the research team considered that if the collision was instead between a white dwarf star and neutron star, it would fit their observations and analysis as it:

· Would provide enough energy to generate the luminosity of calcium rich transients.

· The presence of a white dwarf would provide a mechanism to produce calcium rich material.

· The presence of the Neutron star could explain why this binary star system was found so far from a host galaxy.

“What we therefore propose is these are systems that have been ejected from their galaxy. A good candidate in this scenario is a white dwarf and a neutron star in a binary system. The neutron star is formed when a massive star goes supernova. The mechanism of the supernova explosion causes the neutron star to be `kicked' to very high velocities (100s of km/s). This high velocity system can then escape its galaxy, and if the binary system survives the kick, the white dwarf and neutron star will merge causing the explosive transient.”

The researchers note that such merging systems of white dwarfs and neutron stars are postulated to produce high energy gamma-ray bursts, motivating further observations of any new examples of calcium rich transients to confirm this. Additionally, such merging systems will contribute significant sources of gravitational waves, potentially detectable by upcoming experiments that will shed further light on the nature of these exotic systems.

R.P. Church and M.B. Davies of the Lund University Observatory, Department of Astronomy and Theoretical Physics and N.R.Tanvir of the Department of Physics and Astronomy, University of Leicester made significant contributions to the work in addition to the University of Warwick researchers.

Notes for Editors:

· The work used observations made with the ESO Telescopes at the Paranal Observatory under programme ID 092.D-0420 and the NASA/ESA Hubble Space Telescope, with obtained from the data archive at the Space Telescope Science Institute.

· The University of Warwick acknowledges the support from the UK Science and Technology Facilities Council (grant ID ST/I001719/1).


NASA's Great Observatories Help Astronomers Build a 3D Visualization of Exploded Star

In the year 1054 AD, Chinese sky watchers witnessed the sudden appearance of a "new star" in the heavens, which they recorded as six times brighter than Venus, making it the brightest observed stellar event in recorded history. This "guest star," as they described it, was so bright that people saw it in the sky during the day for almost a month. Native Americans also recorded its mysterious appearance in petroglyphs.

Observing the nebula with the largest telescope of the time, Lord Rosse in 1844 named the object the "Crab" because of its tentacle-like structure. But it wasn't until the 1900s that astronomers realized the nebula was the surviving relic of the 1054 supernova, the explosion of a massive star.

Now, astronomers and visualization specialists from the NASA's Universe of Learning program have combined the visible, infrared, and X-ray vision of NASA's Great Observatories to create a three-dimensional representation of the dynamic Crab Nebula. Certain structures and processes, driven by the pulsar engine at the heart of the nebula, are best seen at particular wavelengths.


Is there a term to describe all stars that are not neutron stars or white dwarfs? - Astronomy

I was wondering about the sizes of white dwarf and neutron stars. The problem is not their size per se, but what happens when you add matter to them.

For example, if a white dwarf star is in a binary system with a red giant that is loosing matter which is added to the white dwarf, how does the size of the white dwarf change over time. Does the added matter make it larger until there is so much mass that it collapses into a neutron star or does the added mass make it shrink even more since there is now more mass to hold up? I think the same analogy can be used with a neutron star getting mass, eventually turning into a black hole. How does it's size change as mass is added? I also thought that the size remains the same but I have no idea how. My question would be, What happens to the size of these type of stars when matter is added?

These are very interesting questions, and the answer is a little complicated and differs whether you're talking about something happening "in principle," or in "the real world." White dwarfs (WDs) and neutron stars (NSs) are two of a class of objects, the "inert self-gravitators," which support themselves against gravitational collapse by force of gas pressure alone. In this context, "gas" can mean either the kind of gas we're used to, or the degenerate matter found in WDs and NSs. Other objects in this class include brown dwarfs and giant planets. In fact, if you disregard chemical composition and think only about the gravity and pressure, giant planets can be considered to be very low-mass white dwarfs. The physics is very similar.

So let's consider a small giant planet, like Neptune. That planet is supported entirely by gas and degeneracy pressure. If we were to slowly add mass to Neptune, the planet would begin to grow in radius. The gravity and pressure would increase as well, of course, but not enough to offset the increase in volume. This will keep occurring until our planet is a few tens or hundreds the size of Jupiter. At that point, the increase in gravity and pressure overcomes the extra volume of mass we add, and the object begins getting smaller. (Remember that we're adding inert mass here--- if we were to add fusionable hydrogen, we'd have a fusing star a totally different story!) Eventually, when you have added a solar mass or so, you end up with an object about the size of the Earth: a white dwarf.

So the answer to your question is that for objects less massive than Jupiter, adding mass increases their size. For objects more massive than Jupiter, adding even more mass decreases their size due to increased gravity and pressure. Since WDs and NSs are much more massive than Jupiter, their sizes decrease with increasing mass.

In practice, when a binary dumps material onto a white dwarf, a nova will occur, sending most of the added material back out into space. If a white dwarf does, however, gain enough mass through this process, it will collapse in a supernova type I. The supernova is probably too powerful to leave a neutron star behind the white dwarf is blown apart. On the other hand, a neutron star which accretes too much mass will indeed collapse into a black hole.

This page was last updated June 27, 2015.

About the Author

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.


What are the similarities and differences between pulsars, quasars, white dwarfs, neutron stars and black holes?

Pulsars, white dwarfs, neutron star and black holes are the remains of dead stars, quasars are powered by black holes.

Explanation:

When a star less than about 8 solar masses runs out of hydrogen and helium fuel, its core isn't hot enough to start carbon fusion. The core which consists of mainly carbon and oxygen collapses under gravity to form a white dwarf. Gravitational collapse is stopped by electron degeneracy pressure.

If the star is larger than about 8 solar masses it is able to fuse heavier elements up to iron. As iron fusion required energy rather than releasing it the fusion reactions stop and the stellar core collapses under gravity. It the core is more massive than the Chandrasekhar limit of 1.44 solar masses gravity overcomes electron degeneracy pressure atoms can no longer exist. Protons become neutrons and large numbers of neutrinos are emitted causing a supernova explosion. The star's core become a neutron star.

If a neutron star is spinning and has a strong magnetic field it emits radiation. As it spins at a precise rate the beam of radiation its the Earth periodically with a period of milliseconds to seconds. This is a pulsar.

If the stellar core is more than about 4 solar masses gravity overcomes neutron degeneracy pressure. Once the core collapses below its Schwarzschild radius, spacetime is curved to the point where not even light can escape. This is a black hole.

Most large galaxies have a supermassive black hole at their centres. These are in excess on hundreds of thousands of solar masses. If there is a good supply of gas and dust in the vicinity of a supermassive black hole it forms an accretion disc of material falling into the black hole. Material falling into the accretion disc gets superheated by friction and gravity to the point where it emits huge amounts of energy. This is a quasar.

So, all are similar in that they are formed from the remains of dying stars. Pulsars are a type of neutron star. Neutron stars and black holes behave similarly. The main difference between these objects is mass.


Answers and Replies

I don't believe you can have a neutron star that light.

Before discussing why something is true, we first need to understand if it is true.

I don't believe you can have a neutron star that light.

Before discussing why something is true, we first need to understand if it is true.

The masses of the component stars have greater uncertainty. The larger (m1) has a 90% chance of being between 1.36 and 2.26 M☉, and the smaller (m2) has a 90% chance of being between 0.86 and 1.36 M

AFAIK our current understanding of the equation of state of neutron star matter does not rule this out I believe it allows neutron stars as light as about 1/10 of a solar mass to be stable. But our current understanding of the equation of state of neutron star matter is not very good.

J0453+1559 has what might be a NS at M = 1.174 (with a 0.4% uncertainty). It could be a WD, although the orbit better fits a NS. Apart from that, the distribution of neutron stars is in the 1.1-2.0 solar mass range.

Using a measurement of 1.11 solar masses with a 23% uncertainty as evidence for M < 1 is just silly.

Peter is right, many EOS's allow for stable neutron star matter at M

0.1. However, these require cold neutron star matter. For hot neutron stars - that is to say, all of them - the limit is close to M = 1. (Indeed, this is one of the reasons we don't know the EOS well. All EOS's under consideration have similar predictions for hot NS matter). So even if a smaller object would be stable, there is no known way to form one, nor do there appear to be any observed.

More precisely, all of them that we have observed. That might be because all of the neutron stars we have observed are fairly young ones--that is, the supernovas that formed them were fairly recent, on cosmological time scales. (The Crab Nebula pulsar, for example, is about 1000 years old.) As these objects age and grow colder, they will get harder to observe, at least with our current technology.

However, it's also true that the main process we are aware of for forming neutron stars--a supernova--requires a star significantly more massive than the Sun (somewhere about 2 to 3 solar masses). A fair fraction of that mass gets ejected during the explosion, but that still leaves a remnant of about 1 solar mass or so. So even a cold neutron star that is a remnant from a supernova that happened billions of years ago would not, on cosmological grounds, be expected to be much ligher than 1 solar mass. I don't know if other mechanisms for forming neutron stars have been proposed that could make cold neutron stars significantly lighter than 1 solar mass.

That sounds strange. What is a temperature which would remove degeneration in the cores of neutron stars? For any temperature much below that scale the temperature should not matter a lot.

Let me know why I am wrong.

That's not actually the case. There are young pulsars, like the Crab and Vela, that are in the process of shedding their initial angular momentum. But there are other pulsars (so-called millisecond pulsars, although this term is misleading) that have been spun back up. Dating them is not easy all we can do is date their companion stars. Typical ages are in the billions of years.

There are about 200 of these known. None have a mass below 1.1-1.2. So if there are smaller NSs out there, why haven't we seen any spun up?

As I mentioned earlier, there's no known formation mechanism. This may not adequately explain the difficulty. To make one of these, you need to squeeze it without heating it. Gravity will not do that for you. You need a non-gravitational squeezing mechanism that can radiate energy faster than thermal radiation. Good luck finding one of those.

Some fraction of these objects will be in binaries, so you have the possibility of SNa 1a equivalents. Nothing like that is visible.

AFAIK our current understanding of the equation of state of neutron star matter does not rule this out I believe it allows neutron stars as light as about 1/10 of a solar mass to be stable. But our current understanding of the equation of state of neutron star matter is not very good.

There is one natural process to remove mass from a neutron star. When the matter from the surface of neutron star starts to spill over to another neutron star or a black hole, and escape on the other side.

But because the neutron stars expand on removal of mass, as a neutron star starts losing mass it expands causing further mass to spill over. The timescale of that process? A neutron star is in the region of 10 km across. Speed of sound is in the region of 100 000 km/s. So the timescale is hundreds of microseconds.

How does the timescale of neutron star expansion compare against timescale of beta decay? Urca process cooling?

What precisely has a neutron star merger to reveal about equation of state of nuclear matter, cold and hot?

The smaller neutron star is cooled by adiabatic expansion.

And decay of neutrons necessarily releases both antineutrinos and heat.

Heat may go to adiabatic expansion, electromagnetic radiation or Urca process. which unlike beta decay produces both antineutrinos and neutrinos.

In the milliseconds after GW170817 started spilling over, the bigger neutron star must have immediately got hot and started emitting both thermal electromagnetic and Urca process. On the other hand, a black hole is, well, black, and therefore will NOT produce Urca process neutrinos.

How efficient is the expanded, spilt-over neutron matter in producing neutrinos by Urca process, as opposed by producing antineutrinos by beta decay?

Also, a black hole has no hair. A neutron star has hair. Oscillations of an actual matter neutron star with no event horizon should produce gravity waves completely different from the ringdown of a structureless black hole, and sensitive to the actual equation of state of the interior.


Is there a term to describe all stars that are not neutron stars or white dwarfs? - Astronomy

Ordinary matter, or the stuff we and everything around us is made of, consists largely of empty space. Even a rock is mostly empty space. This is because matter is made of atoms. An atom is a cloud of electrons orbiting around a nucleus composed of protons and neutrons.

The nucleus contains more than 99.9 percent of the mass of an atom, yet it has a diameter of only 1/100,000 that of the electron cloud. The electrons themselves take up little space, but the pattern of their orbit defines the size of the atom, which is therefore 99.9999999999999% open space!

What we perceive as painfully solid when we bump against a rock is really a hurly-burly of electrons moving through empty space so fast that we can't see—or feel—the emptiness. What would matter look like if it weren't empty, if we could crush the electron cloud down to the size of the nucleus? Suppose we could generate a force strong enough to crush all the emptiness out of a rock roughly the size of a football stadium. The rock would be squeezed down to the size of a grain of sand and would still weigh 4 million tons!

Such extreme forces occur in nature when the central part of a massive star collapses to form a neutron star. The atoms are crushed completely, and the electrons are jammed inside the protons to form a star composed almost entirely of neutrons. The result is a tiny star that is like a gigantic nucleus and has no empty space.

Neutron stars are strange and fascinating objects. They represent an extreme state of matter that physicists are eager to know more about. Yet, even if you could visit one, you would be well-advised to turn down the offer.

The intense gravitational field would pull your spacecraft to pieces before it reached the surface. The magnetic fields around neutron stars are also extremely strong. Magnetic forces squeeze the atoms into the shape of cigars. Even if your spacecraft prudently stayed a few thousand miles above the surface neutron star so as to avoid the problems of intense gravitational and magnetic fields, you would still face another potentially fatal hazard.

If the neutron star is rotating rapidly, as most young neutron stars are, the strong magnetic fields combined with rapid rotation create an awesome generator that can produce electric potential differences of quadrillions of volts. Such voltages, which are 30 million times greater than those of lightning bolts, create deadly blizzards of high-energy particles.

These high-energy particles produce beams of radiation from radio through gamma-ray energies. Like a rotating lighthouse beam, the radiation can be observed as a pulsing source of radiation, or pulsar. Pulsars were first observed by radio astronomers in 1967. There are now approximately 1000 known pulsars. The pulsar in the Crab Nebula, one of the youngest and most energetic pulsars known, has been observed to pulse in almost every wavelength—radio, optical, X-ray, and gamma-ray. A few dozen pulsars are observed to pulse in X-rays and six are seen to pulse in gamma-rays.


These illustrations show how an extremely rapidly rotating neutron star, which has formed from the collapse of a very massive star, can produce incredibly powerful magnetic fields. These objects are known as magnetars.

Magnetars are neutron stars with magnetic fields that are about a quadrillion times greater than the magnetic field of Earth. These awesome magnetic fields are thought to be produced when an extremely rapidly rotating neutron star is formed by the collapse of the core of a massive star. When a neutron star forms it triggers a supernova explosion that expels the outer layers of the star at high speeds.

The high rate of the rotation of the neutron star intensifies the already superstrong magnetic field to magnetar levels. When the magnetic forces get strong enough, they may cause starquakes on the surface of the neutron star that produce powerful outbursts of X-rays called X-ray flashes. These events may represent an intermediate type of supernova explosion - more energetic than ordinary supernovae, but less so than hypernovae, thought to be responsible for gamma ray bursts. Magnetar outbursts can also occur for hundreds of years after the initial explosion.

The strongest steady magnetic field produced on Earth in a lab is about a million times greater than the Earth's magnetic field. Beyond this limit ordinary magnetic material would be blown apart by magnetic forces. Only on a neutron star, where gravity is more than 100 billion times as great as on Earth, can matter withstand the magnetic forces of a magnetar, and even there the neutron star's crust can break apart under the strain.

The source of the power is the rapidly rotating magnetic field, so these pulsars are sometimes called rotationally powered pulsars, to distinguish them from another type of pulsar discovered by X-ray astronomers, the accretion powered pulsars.


Accretion powered pulsars

If a neutron star is in a close orbit around a normal companion star, it can capture matter flowing away from that star. This captured matter will form a disk around the neutron star from which it will spiral down and fall, or accrete, onto the neutron star.

The infalling matter will gain an enormous amount of energy as it accelerates. Much of this energy will be radiated away at X-ray energies. The magnetic field of the neutron star can funnel the matter toward the magnetic poles, so that the energy release is concentrated in a column, or spot of hot matter. As the neutron star rotates, the hot region moves into and out of view and produces X-ray pulses.

If you have a java enabled browser, you can view our animation and discussion of X-ray pulsars.

Accretion-powered pulsars are produced by matter flowing onto the neutron star, whereas rotation-powered pulsars produce an outflow of matter. (In some cases, a significant contribution to the X-ray emission can be from polar caps heated by "instreaming" particles.) For the latter, rapid rotation is required. For the former, an abundant source of infalling gas, such as a companion star is needed. (See Binary and Multiple Star Systems)

Some of the strongest X-ray sources in our galaxy are accreting neutron stars in binary star systems. With Chandra, astronomers have detected hundreds of such objects in other galaxies as well. Accreting neutron stars exhibit various behaviors thought to be related to the details of how the matter falls onto the neutron star. Some pulse steadily, some flicker in a quasi-periodic way, some burst explosively, some eject jets of high-energy particles. If you have a java-enabled browser, you can view our animation and discussion of X-ray pulsars.

A black hole in a binary system could also produce an accretion-powered source. Since black holes do not have a surface or a magnetic pole in the normal sense of the word, they cannot produce regular X-ray pulses, though they may flicker.


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The answer has to do with Ovid. And Shakespeare. And Thomas Edison. And Mary Pickford. Stars are stars, certainly, because they sparkle and shine—because, even when they are bathed in the limelight, they seem to have an incandescence of their own. But they are “stars,” much more specifically, because they are part of Western culture’s longstanding tendency to associate the human with the heavenly. They are “stars” because their audiences want them—and in some sense need them—to be.

The broad use of the word “star” to indicate a leader among us dates back, Peter Davis, a theater historian at the University of Illinois at Urbana-Champaign, told me, to the Middle Ages. Chaucer, who was also the first recorded user of the word “celebrity” and one of the first to use the word “famous,” also hinted at the lexical convergence of the human and the celestial: In The House of Fame, Chaucer’s dreamer worries that he might find himself “stellified.” “O God Who made nature,” the dreamer thinks, “am I to die in no other way? Will Jove transform me into a star?”

Chaucer, Dean Swinford points out in his book Through the Daemon’s Gate, was recalling Ovid’s notion of metamorphosis—the idea that humans could be transformed, in this case, into the shiny stuff of constellations. Chaucer’s words also carried architectural implications that would likely have been apparent to his audiences: “Fixing with stars,” Swinford points out, “implies the creation of a mosaic-like decoration of the interior of a cathedral.” The building was an intentional mimicry of the sky, and an unintentional anticipation of Hollywood’s own kind of firmament: It presented stars as a constellation of gleaming lights, always above.

The US Weeklyfied version of stellification is in many ways a direct descendant of Chaucer’s: It emphasizes the role of the celebrity as a body both distant and accessible, gleaming and sparkling and yet reassuringly omnipresent. Stars have long suggested a kind of order—and orientation—within chaotic human lives. They have long hinted that there is something bigger, something beyond, something more.

Little surprise, then, that—especially as the world of science became more familiar with the workings of celestial bodies—the world of the theater seized on their symbolism. Molière, Peter Davis told me, made Chaucerian use of the personified “star”: In School for Wives, in 1662, Horace describes Agnes as “this young star of love, adorned by so many charms.” Shakespeare, too, neatly anticipated Hollywood’s blending of the personal and the celestial in both his plays and his poems. “We make guilty of our disasters the sun, the moon, and stars,” Edmund laments in King Lear, “as if we were villains on necessity, fools by heavenly compulsion.” Love, too, in Shakespeare’s mind, makes its highest sense as a heavenly force, reassuring in its constancy: In “Sonnet 116,” the bard finds love to be “. an ever-fixed mark / That looks on tempests and is never shaken / It is the star to every wand’ring bark, / Whose worth’s unknown, although his height be taken.”

It was in this context, Davis explains, that the notion of the human star came to refer, in particular, to the decidedly grounded firmament of the theater—and to the decidedly human person of the actor. According to the Oxford English Dictionary, the first reference to a “star” of the stage came in 1751, with the Bays in Council announcing, “You may Shine the brightest Theatric Star, that ever enliven’d of charm’d an Audience.” Around the same time, in 1761, the book Historical Theatres of London & Dublin noted of an apparently Meryl Streepian actor named Garrick: “That Luminary soon after became a Star of the first Magnitude.” Garrick would appear again in 1765, in an extremely effusive article written about him in The Gentleman’s and London Magazine: “The rumor of this bright star appearing in the East flew with the rapidity of lightening through the town, and drew all the theatrical Magi thither to pay their devotions to his new-born son of genius….”

By the 1820s, it was common to refer to actors as “stars”—for purposes of salesmanship as much as anything else. Theater touring became popular during that time, in both England and America. British actors, in particular, Davis told me, were often promoted as “stars” for their tours in the U.S. as a way to ensure that large audiences would come to witness their performances. Actors like Edmund Kean, George Frederick Cooke, and Charles and Fanny Kemble were celestially sold to American audiences. Sometimes, Davis notes, the actors were considered to have passed their prime in Britain they used their American tours to reboot their careers back home. It was fitting: Through the wily dynamics of public relations, “star,” in the U.S., was born.

The term carried through as theater acting gave way to movie acting—as silent films gave way to talkies. “The observable ‘glow’ of potential stardom was present from the very beginning of film history,” Jeanine Basinger notes in her book The Star Machine. But it also took hold, as with so much else in Hollywood history, fitfully. As Jan-Christopher Horak, the director of the UCLA Film and Television Archive, told me, the earliest films didn’t name the actors who starred in them. That was in part because the actors, many of whom had been trained in the theater, were initially embarrassed to be putting their hard-won skills to the service of this strange new medium.

It was also, however, because of the mechanics of the medium itself. On film, Anne Helen Petersen suggests in her book Scandals of Classic Hollywood: Sex, Deviance, and Drama From the Golden Age of American Cinema, the Hollywood star was a function of technology as much as it was one of culture. As early cinema developed in the early 20th century, bulky and unwieldy cameras made it difficult for cinematographers to capture anything beyond full-length shots of actors. “Because viewers couldn’t see the actor’s face up close,” Petersen writes, “it was difficult to develop the feelings of admiration or affection we associate with film stars.” As cameras improved, though, close-ups became more common, emphasizing actors’ faces and humanity. As sound became part of the cinema experience, voices, too, substituted full personas for lurching images. The “picture personality” had arrived. The “star,” yet again, was born.

With that came the star system that would give structure to Hollywood for much of its young life. Mary Pickford, Horak notes, one of the first movie actors to be billed under her (stage) name, soon began making films under her own banner. Charlie Chaplin, long before Andy Warhol would ironize the term, became a superstar. The star itself, in the era of spotlights and marquis banners, soon became a metonym—a convenient and fitting way to describe the people who studded Hollywood’s new and expanding firmament. The term that had taken life in the age of Shakespeare and Molière and early romanticism—a time that would, in some places, find art becoming obsessed with the dignity of the individual and the fiery workings of the human soul—came alive yet again in the glow of the screen.

It may be quaint, today, to talk of “movie stars.” This is an age defined, after all, by that other Chaucerian term: the “celebrity.” It’s an age of actor-founded lifestyle brands and internet-famous felines and people starring in reality itself. But our current celebrities, too, suggest something similar to what “star” has long evoked: orientation, transcendence, a kind of union between mortals and the gods they have chosen for themselves. “Celebrity” comes from the Old French for “rite” or “ceremony” it suggests that even the most frivolous of the famous are filling a role that is, in its way, profound. Stars—fusions of person and persona, of the fleshy human and the flinty image on the stage and screen—have long offered a kind of structure within the hectic hum of human lives. They have long promised that most basic and inspiring of things: that we can be something more than what we are. “I am big,” Norma Desmond, that fading star, insisted. “It’s the pictures that got small.”


Interesting Facts About Stars

Think you know everything there is to know about stars? Think again! Here’s a list of 10 interesting facts about stars some you might already know, and few that are going to be new.

1. The Sun is the closest star

Okay, this one you should know, but it’s pretty amazing to think that our own Sun, located a mere 150 million km away is average example of all the stars in the Universe. Our own Sun is classified as a G2 yellow dwarf star in the main sequence phase of its life. The Sun has been happily converting hydrogen into helium at its core for 4.5 billion years, and will likely continue doing so for another 7+ billion years. When the Sun runs out of fuel, it will become a red giant, bloating up many times its current size. As it expands, the Sun will consume Mercury, Venus and probably even Earth. Here are 10 facts about the Sun.

2. Stars are made of the same stuff

All stars begin from clouds of cold molecular hydrogen that gravitationally collapse. As they cloud collapses, it fragments into many pieces that will go on to form individual stars. The material collects into a ball that continues to collapse under its own gravity until it can ignite nuclear fusion at its core. This initial gas was formed during the Big Bang, and is always about 74% hydrogen and 25% helium. Over time, stars convert some of their hydrogen into helium. That’s why our Sun’s ratio is more like 70% hydrogen and 29% helium. But all stars start out with 3/4 hydrogen and 1/4 helium, with other trace elements.

3. Stars are in perfect balance

You might not realize but stars are in constant conflict with themselves. The collective gravity of all the mass of a star is pulling it inward. If there was nothing to stop it, the star would just continue collapsing for millions of years until it became its smallest possible size maybe as a neutron star. But there is a pressure pushing back against the gravitational collapse of the star: light. The nuclear fusion at the core of a star generates a tremendous amount of energy. The photons push outward as they make their journey from inside the star to reach the surface a journey that can take 100,000 years. When stars become more luminous, they expand outward becoming red giants. And when they run out of light pressure, they collapse down into white dwarfs.

4. Most stars are red dwarfs

If you could collect all the stars together and put them in piles, the biggest pile, by far, would be the red dwarfs. These are stars with less than 50% the mass of the Sun. Red dwarfs can even be as small as 7.5% the mass of the Sun. Below that point, the star doesn’t have the gravitational pressure to raise the temperature inside its core to begin nuclear fusion. Those are called brown dwarfs, or failed stars. Red dwarfs burn with less than 1/10,000th the energy of the Sun, and can sip away at their fuel for 10 trillion years before running out of hydrogen.

5. Mass = temperature = color

The color of stars can range from red to white to blue. Red is the coolest color that’s a star with less than 3,500 Kelvin. Stars like our Sun are yellowish white and average around 6,000 Kelvin. The hottest stars are blue, which corresponds to surface temperatures above 12,000 Kelvin. So the temperature and color of a star are connected. Mass defines the temperature of a star. The more mass you have, the larger the star’s core is going to be, and the more nuclear fusion can be done at its core. This means that more energy reaches the surface of the star and increases its temperature. There’s a tricky exception to this: red giants. A typical red giant star can have the mass of our Sun, and would have been a white star all of its life. But as it nears the end of its life it increases in luminosity by a factor of 1000, and so it seems abnormally bright. But a blue giant star is just big, massive and hot.

6. Most stars come in multiples

It might look like all the stars are out there, all by themselves, but many come in pairs. These are binary stars, where two stars orbit a common center of gravity. And there are other systems out there with 3, 4 and even more stars. Just think of the beautiful sunrises you’d experience waking up on a world with 4 stars around it.

7. The biggest stars would engulf Saturn

Speaking of red giants, or in this case, red supergiants, there are some monster stars out there that really make our Sun look small. A familiar red supergiant is the star Betelgeuse in the constellation Orion. It has about 20 times the mass of the Sun, but it’s 1,000 times larger. But that’s nothing. The largest known star is the monster VY Canis Majoris. This star is thought to be 1,800 times the size of the Sun it would engulf the orbit of Saturn!

8. The most massive stars are the shortest lived

I mentioned above that the low mass red dwarf stars can sip away at their fuel for 10 trillion years before finally running out. Well, the opposite is true for the most massive stars that we know about. These giants can have as much as 150 times the mass of the Sun, and put out a ferocious amount of energy. For example, one of the most massive stars we know of is Eta Carinae, located about 8,000 light-years away. This star is thought to have 150 solar masses, and puts out 4 million times as much energy. While our own Sun has been quietly burning away for billions of years, and will keep going for billions more, Eta Carinae has probably only been around for a few million years. And astronomers are expecting Eta Carinae to detonate as a supernovae any time now. When it does go off, it would become the brightest object in the sky after the Sun the Moon. It would be so bright you could see it during the day, and read from it at night.

9. There are many, many stars

Quick, how many stars are there in the Milky Way. You might be surprised to know that there are 200-400 billion stars in our galaxy. Each one is a separate island in space, perhaps with planets, and some may even have life. But then, there could be as many as 500 billion galaxies in the Universe, and each of which could have as many or more stars as the Milky Way. Multiply those two numbers together and you’ll see that there could be as many as 2 x 10 23 stars in the Universe. That’s 200,000,000,000,000,000,000,000.

10. And they’re very far

With so many stars out there, it’s amazing to consider the vast distances involved. The closest star to Earth is Proxima Centauri, located 4.2 light-years away. In other words, it takes light itself more than 4 years to complete the journey from Earth. If you tried to hitch a ride on the fastest spacecraft ever launched from Earth, it would still take you more than 70,000 years to get there from here. Traveling between the stars just isn’t feasible right now.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?


IRA FLATOW: For decades, astronomers have been puzzling over the mystery of ULXs. Those are Ultra Luminous X-ray sources– of course you knew that– often perched in the edges of galaxies, not quite strong enough to be super-massive black holes, but too bright to be other kinds of known objects. Well, four years ago, the mystery seemed solved.

The fledgling NuSTAR telescope detected pulsations that proved at least a few of them were neutron stars. Neutron stars– tiny dense stars that pack the mass of several suns into the space of just a few kilometers. But that just created a new problem, because these neutron stars were far brighter than they should be– given what we know about the limitations of mass and luminosity in stars, hundreds of times too bright, the kind of a problem astronomers love to have.

Well, now new research might have an answer. These neutron stars might have an intensely-powerful magnetic field, 10 billion times the strongest magnetic field we’ve ever generated on Earth. The research is published in Nature Astronomy this week. And my guest, Dr. Matt Middleton, a lecturer in physics and astronomy at the University of Southampton in UK is one of the co-authors. Welcome, Dr. Middleton, to Science Friday.

MATT MIDDLETON: Hi, there. Thank you for having me on.

IRA FLATOW: So what made these X-ray sources so mysterious?

MATT MIDDLETON: Right. So the mystery really goes back to the 1970s, when people first started looking out into the universe with X-ray telescopes. Because remember, you can’t actually see X-ray bright objects on the Earth, because– thankfully– our atmosphere protects us from such harmful radiation. And when people looked out, they found these things that were really, really bright. They were far too bright than they had any right to be, really.

They weren’t associated with the centers of galaxies, where we know material falls onto these super-massive black holes, where the mass is millions of billions times the mass of the sun. But they were still way too bright to be what we normally see in X-ray binaries, where we have a black hole which is, say, 10 times the mass of the sun, or a neutron star, which is around 1 to 1.4 time the mass of the sun, or even white dwarfs, which can be even more tiny. But they’re really, really gravitationally-compact objects. And material falls onto them. And they get very bright.

But these ULXs, they seem to be too bright for that. So for a long time, astronomers were sort of scratching their heads and going, well, what could this be? And people first thought, OK, well, maybe these are a new type of gravitationally-compact objects. And maybe these are what we’ll call intermediate mass black holes, which is a great idea, right? Because we know that super-massive black holes in the centers of basically all galaxies had to form somehow. So they had to build themselves up from very, very small, possibly primordial black holes.

And somewhere along that line, there may have been intermediate mass black holes, around 100, 1,000, 10,000 times the mass of the sun. So maybe that’s what they were. But we can’t just go and weight these things. It’s very, very difficult. So we needed indirect evidence to work out what they were.

And so for a very long time this argument in the community raged, on what are they? Do we think they’re normal, stellar mass compact objects? Or do we think they’re intermediate mass black holes? So that was really the root of all these arguments.

IRA FLATOW: So voila– you look at your data. And you say, they’re not black holes. They are a different kind of neutron star that we’ve not seen before?

MATT MIDDLETON: Well, so it’s slightly more complicated than that. So we looked at them, and the evidence wasn’t clear cut. So we looked at what we call the X-ray spectra and their variability. So the spectrum is where you break your light into various different channels. And you look at the shape of that. And you can compare that to objects that we know and study really well.

And for a long time we looked at them and we thought, well, we don’t really know what these look like. They could be intermediate mass black holes. Or they could be stellar mass black holes. Maybe they could be neutron stars. We don’t really know. We all had to come up with indirect lines of thought to get there.

And then all of a sudden, things got much simpler, because a colleague of ours, Matteo Bachetti, discovered with the NuSTAR telescope– which is led by Fiona Harrison, who I know you’ve had on the show before– they discovered these pulsations. And these positions indicated that this thing had to have a surface. And it was spinning really quickly. So all of a sudden they thought, well, it can’t be a black hole, because black holes don’t have surfaces.

MATT MIDDLETON: Although hypersurface is a different topic altogether. So it had to be neutron star. And then the question is, how can these neutron stars be so bright?

IRA FLATOW: And then your answer was, well, we give them this giant magnetic field.

MATT MIDDLETON: So there’s two ways to do it two ways to skin this cat. You can either put a lot of material at very, very rapid rates towards a neutron star. And then what happens– at a certain radius, in what we call an accretion disk, so imagine a pancake. And in the middle of that pancake you’ve got a neutron star. At some radius, or some distance from the neutron star, the disk puffs up. And then it tapers down to the neutron star, so in a bit of a cone, right?

MATT MIDDLETON: And then all that radiation that’s produced within that disk or from that neutron star gets trapped within that cone. And it gets what we call geometrically beamed towards us. So it’s like having a flashlight. It’s mirrored behind it, so that it reflects that illumination that’s coming from the bulb back out towards you. That’s why it looks so much brighter than it would do if you just had the bulb on it’s own. So that’s one way you can do it.

The other way you can do it is by having, as you said, a really, really strong magnetic field. And it’s possible the truth lies somewhere in between. The importance of the magnetic field in this picture is that it reduces what we call the cross-section, or the scattering cross-section to electrons.

And that’s horribly complicated. So let me just say what I mean there. What we define as the Eddington limit is the point at which radiation– so the push by light is balanced by gravity. And that push by light is related to what those photons in that light can scatter off. It’s called a cross-section, OK?

So that cross-section changes. If it becomes smaller, then you can put more material onto your neutron star or your black hole. And so you can essentially generate more luminosity that way. So there are two ways to do it. You either have geometrical beaming or you have a very, very strong magnetic field. And those are really the two options that people have been investigating.

IRA FLATOW: Mm-hmm. This is Science Friday from PRI, Public Radio International. Talking with Matt Middleton, lecturer in physics and astronomy at the University of Southampton in the UK. You know, black holes get so much attention, don’t they?

IRA FLATOW: Do you neutron star guys get a little jealous of not giving enough neutron star love out there to these stars?

MATT MIDDLETON: Oh, there’s so much neutron star love. There’s so much neutron star love. You know, a big shout-out to all my people who work on ultra-dense matter. I think the thing is that black holes are fundamentally very sexy. You know, look at films like Interstellar. And if you’re old enough, you might remember a Disney film called Black Hole.

It’s very easy– because they’re quite scary things and they’re quite cool. They’re beyond what we can conceptualize. Neutron stars are very difficult to conceptualize. But they are essentially a star. So you can picture that in your head. A black hole is shrunk down beyond the [INAUDIBLE]. It’s so small you have to invoke quantum gravity and all sorts of weird effects.

But the neutron star community is so alive and effervescent. And they’re working all sorts of fantastic things, including ultra-dense matter, which is something we can never really probe on Earth. So the physics that they’re doing, you can’t really approach through any other means. So I don’t think the neutron star guys are upset by black hole astrophysicists and the results that we get out.

I think maybe black hole guys sometimes wish there was a surface, because those have their own very special effects. And sometimes neutron star guys probably think, wow, I really wish this thing didn’t have a surface. It’d make things in my life a lot easier.

MATT MIDDLETON: But they’re different bits of science, and both of them extremely interesting.

IRA FLATOW: Of course, last year’s big gravitational wave news was that LIGO and Virgo had detected these colliding neutron stars–

IRA FLATOW: Something we’ve never observed before. Is there something else like that we might soon have a chance to observe?

MATT MIDDLETON: Yeah, sure. Well, I mean, so the very first detection was two black holes merging together.

MATT MIDDLETON: And then neutron stars have also been found, which were long expected to be found. And it’s a really interesting question. So the way that you detect gravitational waves is that– well, not the way you detect them, but the way you produce them is having what we call a gravitational quadrupole moment. And lots of things can have gravitational waves. You or I could be producing gravitational waves, just so small we could never detect them.

So who knows what we’re going to find out there. We could be seeing super-massive black holes that are spinning together and merging. We could be looking back at the early times in the universe and looking at the gravitational waves coming from those black holes merging, and then the galaxies being formed and developed around them. We could be finding neutron stars, [? coming out of ?] black holes, or white dwarfs [? coming ?] [? out of ?] neutron stars, all sorts of things. So it’s going to be an extremely interesting and important window we’ve opened to the universe. And I personally feel very, very honored to be part of astronomy in this exciting time, because it’s going to get really interesting.

IRA FLATOW: Because I talk to astronomers and physicists all the time. And what really excites them is that they don’t know something.

MATT MIDDLETON: Yeah, absolutely.

IRA FLATOW: It’s the hunt that they like.

MATT MIDDLETON: Well, of course. I mean, we can’t write papers on what people already know. We’re in it for the mystery, right? And I love astronomy. You know, I grew up watching Star Trek– I mean, obviously, the Patrick Stewart version, you know?

MATT MIDDLETON: But those sort of programs really touched me as a child. And of course I got interested in astronomy and the mysteries that are out there. And yeah, OK, I don’t fly around in a starship. But I can close my eyes and pretend.

MATT MIDDLETON: But I get to work on these amazing objects. And I’m just really fortunate to get to do that.

IRA FLATOW: Well, I’m glad you “engage” in your work.

MATT MIDDLETON: Hell of a pun.

IRA FLATOW: Yeah I know. That’s me. Matt Middleton lectures in physics and astronomy, University of Southampton, and co-author of the new neutron star research. Glad to see you have so much fun with this. Thank you for taking time to be with us today.

MATT MIDDLETON: My pleasure, anytime.

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