Astronomy

Could population III stars develop directly into population I stars?

Could population III stars develop directly into population I stars?


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Hundreds of millions of years after the Big Bang, the very first stars began to form consisting of mostly hydrogen, a bit of helium, and maybe some lithium. These stars lacked any "metals" (elements heavier than helium) and are categorized as Population III stars. We have yet to observe any of these Pop III stars, and observation remains unlikely. The reason for this is because Pop III stars are thought to have been incredibly massive, so they died out so long ago that we can no longer see their light. Pop I stars are metal-rich; their metallicity is 1/10 to 3 times that of our Sun's. In my research, everyone seems to agree that that the first generation of stars had no metal, second generation stars had very little, and third generation stars have some metal.But, no one ever addresses the possibilities. So, is it possible that some Pop III stars were so massive that they were able to skip Pop II and go straight to Pop I? Maybe if several are close by when they go supernova?


No they couldn't. Population I stars contain elements like strontium, barium, gold, lead etc. that are not formed (much) in type II (core collapse) supernovae. They are also much richer in iron, nickel, manganese etc. than are stars formed from gas enriched only by supernovae.

Population I stars (like the Sun) can be termed third generation stars because they contain material that has been through at least two stars - but not just two high mass stars that exploded as supernovae.

Iron-peak elements are mainly formed and disseminated by type Ia supernova that are exploding white dwarfs. White dwarfs are the remnants of low-mass stars with long lives.

Many heavy elements (strontium, barium, lead etc) are formed by the s-process in intermediate mass stars that also have (relatively) long lives and do not explode as supernovae. Furthermore, this neutron capture requires iron-peak nuclei to act as seeds, so these stars must in turn have formed out of material already enriched with iron-peak nuclei.

It is also now thought that other elements (silver, gold, osmium etc) are formed by the merger of neutron stars, where there must be a significant delay between the initial supernovae that produced the neutron stars and the subsequent merger by orbital decay.


Best observational evidence of first generation stars in the universe

Astronomers have long theorised the existence of a first generation of stars -- known as Population III stars -- that were born out of the primordial material from the Big Bang [1]. All the heavier chemical elements -- such as oxygen, nitrogen, carbon and iron, which are essential to life -- were forged in the bellies of stars. This meansthat the first stars must have formed out of the only elements to exist prior to stars: hydrogen, helium and trace amounts of lithium.

These Population III stars would have been enormous -- several hundred or even a thousand times more massive than the Sun -- blazing hot, and transient -- exploding as supernovae after only about two million years. But until now the search for physical proof of their existence had been inconclusive [2].

A team led by David Sobral, from the Institute of Astrophysics and Space Sciences, the Faculty of Sciences of the University of Lisbon in Portugal, and Leiden Observatory in the Netherlands, has now used ESO's Very Large Telescope to peer back into the ancient Universe, to a period known as reionisation, approximately 800 million years after the Big Bang. Instead of conducting a narrow and deep study of a small area of the sky, they broadened their scope to produce the widest survey of very distant galaxies ever attempted.

Their expansive study was made using the VLT with help from the W. M. Keck Observatory and the Subaru Telescope as well as the NASA/ESA Hubble Space Telescope. The team discovered -- and confirmed -- a number of surprisingly bright very young galaxies. One of these, labelled CR7 [3], was an exceptionally rare object, by far the brightest galaxy ever observed at this stage in the Universe [4]. With the discovery of CR7 and other bright galaxies, the study was already a success, but further inspection provided additional exciting news.

The X-shooter and SINFONI instruments on the VLT found strong ionised helium emission in CR7 but -- crucially and surprisingly -- no sign of any heavier elements in a bright pocket in the galaxy. This meant the team had discovered the first good evidence for clusters of Population III stars that had ionised gas within a galaxy in the early Universe [5].

"The discovery challenged our expectations from the start,"said David Sobral, "as we didn't expect to find such a bright galaxy. Then, by unveiling the nature of CR7 piece by piece, we understood that not only had we found by far the most luminous distant galaxy, but also started to realise that it had every single characteristic expected of Population III stars. Those stars were the ones that formed the first heavy atoms that ultimately allowed us to be here. It doesn't really get any more exciting than this."

Within CR7, bluer and somewhat redder clusters of stars were found, indicating that the formation of Population III stars had occurred in waves -- as had been predicted. What the team directly observed was the last wave of Population III stars, suggesting that such stars should be easier to find than previously thought: they reside amongst regular stars, in brighter galaxies, not just in the earliest, smallest, and dimmest galaxies, which are so faint as to be extremely difficult to study.

Jorryt Matthee, second author of the paper, concluded: "I have always wondered where we come from. Even as a child I wanted to know where the elements come from: the calcium in my bones, the carbon in my muscles, the iron in my blood. I found out that these were first formed at the very beginning of the Universe, by the first generation of stars. With this discovery, remarkably, we are starting to actually see such objects for the first time."

Further observations with the VLT, ALMA, and the NASA/ESA Hubble Space Telescope are planned to confirm beyond doubt that what has been observed are Population III stars, and to search for and identify further examples.

[1] The name Population III arose because astronomers had already classed the stars of the Milky Way as Population I (stars like the Sun, rich in heavier elements and forming the disc) and Population II (older stars, with a low heavy-element content, and found in the Milky Way bulge and halo, and globular star clusters).

[2] Finding these stars is very difficult: they would have been extremely short-lived, and would have shone at a time when the Universe was largely opaque to their light. Previous findings include: Nagao, et al., 2008 , where no ionised helium was detected De Breuck et al., 2000, where ionised helium was detected, but alongside carbon and oxygen, as well as clear signatures of an active galactic nucleus and Cassata et al., 2013, where ionised helium was detected, but of a very low equivalent width, or weak intensity, and alongside carbon and oxygen.

[3] CR7's nickname is an abbreviation of COSMOS Redshift 7, a measure of its place in terms of cosmic time. The higher the redshift, the more distant the galaxy and the further back in the history of the Universe it is seen. A1689-zD1 , one of the oldest galaxies ever observed, for example, has a redshift of 7.5.

CR7 is located in the COSMOS field, an intensely studied patch of sky in the constellation of Sextans (The Sextant).

The nickname was inspired by the great Portuguese footballer, Cristiano Ronaldo, who is known as CR7.

[4] CR7 is three times brighter than the previous titleholder, Himiko, which was thought to be one of a kind.

[5] The team considered two alternate theories: that the source of the light was either from an AGN or Wolf-Rayet stars. The lack of heavy elements, and other evidence strongly refutes both these theories. The team also considered that the source may be a direct-collapse black hole, which are themselves exceptional exotic and purely theoretical objects. The lack of a broad emission line and the fact that the hydrogen and helium luminosities were much greater than what has been predicted for such a black hole indicate that this, too, is unlikely. A lack of X-ray emissions would further refute this possibility, but additional observations are needed.


Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?

Here on Earth, the closest world to us is our barren, uninhabited moon. But in many imaginable . [+] cases, there could be another inhabited world close by our own, maybe even within our Solar System. How close could one be?

Here on planet Earth, in orbit around the Sun, we're the only intelligent-life game in town. There might be possibilities for either past life or microbial life elsewhere in the Solar System, but as far as intelligent, complex, differentiated and multicellular life goes, what's on our world is far more advanced than anything else we could hope to find. Intelligent aliens, if they're out there inhabiting another world, are at least four light years away. But must that be the case for aliens anywhere in the galaxy? That's what our Patreon supporter Jason McCampbell wants to know:

What's [the] closest two, independent intelligent civilizations could be, ignoring interstellar travel and assuming they develop in different star systems and follow roughly what we know as 'life'? Globular clusters can have a high density of stars, but does too high a density rule out habitability? An astrophysicist in a dense cluster would have a much different view of the universe and the search for exoplanets.

There are lots of steps that have to happen to make life, but the ingredients for it are literally everywhere. Even if you're restricting yourself to looking for life that looks (chemically) like us, the Universe is full of possibilities.

Atoms can link up to form molecules, including organic molecules and biological processes, in . [+] interstellar space as well as on planets. Is it possible that life began not only prior to Earth, but not on a planet at all?

You need to form enough heavy elements so that you can have rocky planets, organic molecules, and the building blocks of life. The Universe isn't born with these! In the aftermath of the Big Bang, the Universe is 99.999999% hydrogen and helium, with no carbon, no oxygen, no nitrogen, phosphorous, calcium, iron, or any of the other complex elements necessary for life. In order to get there, we have to have multiple generations of stars live, burn through their fuel, die in a supernova explosion, and recycle those newly-created heavy elements into the next generation of stars. We need neutron star-neutron star mergers to build up the heaviest elements, many of which are necessary for life processes here on Earth and in our bodies, in copious amounts. This requires a lot of astrophysics to make it so.

The Omega nebula, known also as Messier 17, is an intense and active region of star formation, . [+] viewed edge-on, which explains its dusty and beam-like appearance. Stars that form at different times in the Universe's history have different abundances of heavy elements.

Even though Earth formed over 9 billion years after the Big Bang, the Universe didn't have to wait so long. We classify stars into three populations:

  • Population I: stars like the Sun, with 1-2% of the elements making them up being heavier than hydrogen and helium. This material is very processed and leads to solar systems with a mix of gas giants and rocky planets capable of housing life.
  • Population II: these are mostly older, more pristine stars. They may only have 0.001-0.1% of the heavy elements the Sun has, and most of their worlds are diffuse, gassy worlds. These may be too primitive and too low in heavy elements for life.
  • Population III: the first stars in the Universe, that must be entirely unpolluted by heavy elements. These haven't yet been discovered, but are theoretically the first stars of all.

When we look at the earliest galaxies, they're full of pretty much all Population II stars. But nearby, we have a mix of young-and-old, metal-rich and metal-poor stars.

The distances between the Sun and many of the nearest stars shown here are accurate, but each star . [+] -- even the largest ones here -- would be less than one-one millionth of a pixel in diameter if this were to scale. Image credit: Andrew Z. Colvin, under a c.c.a.-s.a.-3.0.

Andrew Z. Colvin / Wikimedia Commons

One of the most important lessons came from the Kepler mission, and specifically the system Kepler-444. This is a Population I star (with planets around it), but it's much, much older than Earth. While our world is about 4.5 billion years old, Kepler-444 is 11.2 billion years old, meaning that the Universe could've formed a world like Earth very early on, at least

7 billion years earlier than Earth formed. Given that possibility, and the fact that areas like the center of our galaxy got even more metal-rich than our region did very, very quickly, it's possible that there are locations in the Universe (and perhaps even in the Milky Way) that are even more conducive to bringing about intelligent life than the Sun-Earth system is.

Sugar molecules in the gas surrounding a young, Sun-like star. The raw ingredients for life may . [+] exist everywhere, but not every planet that contains them will develop life.

ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO) & NASA/JPL-Caltech/WISE Team

So given all that we know about where the stars that are good candidates for life can be, what's the closest two alien civilizations could be to one another? Where would be the places to look? And what would the answers be under different circumstances? Let's look at five major possibilities.

This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential . [+] for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. However, it is unknown whether any of these worlds actually still possess atmospheres, or if they've been blown away by their parent star. One thing is certain, however: the potentially habitable worlds are close to each other: separated by only

1.) The same solar system. This is the real dream. In the early days of our Solar System, it's plausible that Venus, Earth, and Mars (and potentially even Theia, the hypothetical planet that collided with Earth to create the Moon) all had the same life-friendly conditions. They likely had a crust and atmosphere full of the ingredients for life, along with a past history of liquid water on their surface. Venus and Mars each, at closest approach to Earth, come within a few tens of millions of kilometers: 38 million for Venus and 54 million for Mars. But around an M-class (red dwarf) star, planetary separation distances are much smaller: separation distances are approximately only 1 million km between potentially habitable worlds in the TRAPPIST-1 system. Twin moons around a giant world, or a binary planet, could be even closer. If life succeeds once given certain conditions, why not twice in almost exactly the same place?

The globular cluster Terzan 5 as seen by the ESO's Very Large Telescope, with other data as well. . [+] The densities in the center of a globular cluster are higher, while still being stable, than anyplace else.

ESO-VLT, F.R. Ferraro et al., HST-NICMOS, ESA/Hubble & NASA

2.) Within a globular cluster. Globular clusters are massive collections of somewhere around hundreds of thousands of star contained within a sphere of perhaps a few dozen light years in radius. In the outer regions, stars are typically separated by a light year, but in the innermost regions of the densest clusters, star separations may be as small as the distance from the Sun to the Kuiper belt. The orbits of planets within those star systems should be stable even in these dense environments, and given that we know of globular clusters far younger than the 11.2 billion years that Kepler-444 is, there should be good candidates for life and habitability among them. A few hundred astronomical units, although this distance will change over time as stars move, could be a fascinatingly close encounter between two civilizations.

High resolution near-infrared imaging has led to the discovery of three stellar superclusters at the . [+] Galactic Center. Since near-infrared wavelengths cut through the dense dust between Earth and the Galactic Center, we are able to see these superclusters. They include the Central Parsec, Quintuplet, and Arches clusters. But all the stars found there, and in the galactic center in general, are quite young.

3.) Near the galactic center. The closer you get to the center of the galaxy, the denser the stars get. Within the central few light years, we have extremely high densities of stars, rivaling what we see in the cores of globular clusters. In some ways, the galactic center is an even denser environment, with large black holes, extremely massive stars, and new star-forming clusters, all things that globular clusters don't have. But the problem with the stars that we see in the Milky Way's core is that they're all relatively young. Perhaps due to the volatility of the environment there, stars rarely make it to even a billion years of age. Despite the increased density, these stars are unlikely to have advanced civilizations. They just don't live long enough.

Stars form in a wide variety of sizes, colors and masses, including many bright, blue ones that are . [+] tens or even hundreds of times as massive as the Sun. This is demonstrated here in the open star cluster NGC 3766, in the constellation of Centaurus.

4.) In a dense star cluster or spiral arm. Okay, so what about the star clusters that form in the galactic plane? Spiral arms are denser than typical regions of a galaxy, and that's where new stars are likely to form. The star clusters that remain from those epochs often contain thousands of stars located in a region just a few light years wide. But again, stars don't remain in these environments for very long. The typical open star cluster dissociates after a few hundred million years, with only a small fraction lasting billions of years. Stars move in-and-out of spiral arms all the time, including the Sun. Overall, even though stars inside may have typical distances between them of between 0.1 and 1 light year, they're unlikely to be good candidates for life.

A logarithmic chart of distances, showing the Voyager spacecraft, our Solar System and our nearest . [+] star, for comparison.

5.) Distributed throughout interstellar space. Otherwise, we come back to what we see in our own neighborhood: distances that are typically a few light years. As you get closer to the center of a galaxy, you can decrease that to the same distance you see in an open cluster: between 0.1-1 light years. But if you try to get closer than that, you run into the problem we've seen too close to the galactic center: mergers, interactions, and other catastrophes are likely to ruin your stable environment. You can get closer, but typical interstellar space isn't the way to go. If you insist on it, your best bet is to wait for another star to pass close by, something that happens about once every million years for a typical star.

A plot of how frequently stars within the Milky Way is likely to pass within a certain distance of . [+] our Sun. This is a log-log plot, with distance on the y-axis and how long you typically need to wait for such an event to happen on the x-axis.

While we don't expect intelligent alien life to be ubiquitous and plentiful throughout the Universe in the same way that planets and stars are, every such world that meets the right conditions is a chance. And every time you get a chance, that's an opportunity, with finite odds, for success. Each one of these possibilities could be real! They may not be likely, but until we go out and find what is (and isn't) out there, it's vital to keep an open mind about what the Universe could bring to us as far as alien intelligence is concerned. The truth is no doubt out there, but it's important to recognize that if we had gotten a lot luckier, it could be closer than we dare to imagine today.


What Were the First Stars?

[/caption]
Astronomers now know that the Big Bang occurred 13.7 billion years ago. For the first few hundred million years, the entire Universe was too hot any stars to form. But then the Universe cooled down to the point that gravity could start pulling together the raw hydrogen and helium into the first ever stars.

The basic elements on the Universe, hydrogen and helium and a few trace elements, we formed during the Big Bang. For a brief moment, the entire Universe was at the temperature and pressure that hydrogen could fuse into helium. This is why we see roughly the same ratios of hydrogen to helium, everywhere we look in the Universe: 73% hydrogen, 25% helium, and the rest are trace elements.

Astronomers think that this pure hydrogen/helium mix allowed the first stars to grow much more massive than stars can get today. It’s believed that they could have gathered together several hundred solar masses. The most massive star that can form today is thought to only be about 150 solar masses. After that point, extreme winds coming from the star prevent any additional material from falling in.

This first generation of stars, which astronomers call Population III stars, would have lived short violent lives. They probably lasted just a million years or so, and then detonated as supernovae. But in their lives, these Population III stars would have created heavier and heavier elements at their cores, and in their violent deaths, they would have created the even more exotic heavier elements, like gold and uranium. It’s possible that the first stars went through a few quick cycles, pulling in material, detonating and seeing the region with heavier elements. Eventually the first long-term stars would have gotten going, stars with the amount of heavier elements we see today.

None of the first stars have ever been observed directly. There have been a few hints through gravitational lensing using a nearby galaxy’s gravity to focus the light from a more distant quasar. The next generation of space telescopes, like the James Webb Space Telescope might be able to push the observable Universe back to these first stars.

We have written many articles about stars here on Universe Today. Here’s an article about astronomers simulating the formation of the first stars, and here’s an article about how the first stars could have been powered by dark matter.

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?


Do they exist?

In the big bang model for star-formation we see a big difference between the story for the first unobservable stars and the stars that are observed today. Keep in mind that about 90% of the stars observed today plot on the main sequence of the H-R star diagram. Of these, the majority (about 70% or more) are less than 0.8 M. However, evolutionists could not tolerate this situation for the Population III stars, otherwise the universe would be filled with numerous examples to observe. Yet, none have been found.

It seems that evolutionists commonly gloss over this part of the story when they attempt to convince the public that they understand the origin of stars (and by implication the origin of people, i.e. carbon, oxygen, and iron in our bodies forged in the stars.) Astronomy recently published some information on the origin of Population III stars:

&lsquoThe problem: If water is crucial in the formation of stars in these clouds, how would the first stars have formed since no water was available?&rsquo 8

The editors answer:

&lsquoAstronomers don&rsquot know for sure how the universe made its first stars, but they do have a reasonably good guess. (As you can imagine, there&rsquos no way to observe the formation of the first generation of stars, so all the work is based upon theoretical considerations.) The best scenario has molecular hydrogen playing the role of the cooling agent. If the clouds from which stars formed were some four to five times denser in the early universe than they are today, then enough collisions between hydrogen atoms would have taken place to create a lot of molecular hydrogen. The big question is: Were the first galaxies that much denser? Obviously the overall density of the universe was much higher back in the early days, but no one knows whether the star-forming clouds were this much denser.

&lsquoMost astronomers would say that the fact that stars do exist tells us that the density was higher back then, because otherwise there would be no stars &hellip Nowadays, of course, nature has found a simpler, easier way to cool the clouds (with water), so that&rsquos what she uses.&rsquo 8

It seems there is a major problem with the answer given:

The term, &lsquohave not yet been identified&rsquo leads to the &lsquobig question&rsquo: Where are examples of these first generation stars or Population III stars? There is no evidence that the universe ever had or does contain Population III stars. There is no evidence that the universe ever contained the primordial star forming clouds that contained no metals. The editors failed to point this out in the &lsquotheoretical&rsquo answer provided. Their answer assumes that Population III stars are real. Indeed, their answer is tantamount to conjecture and circular reasoning based upon the big bang. The editors also failed to identify the critical role of dark matter in the equations of state used to model the formation of Population III stars, as say compared to molecular gas clouds like M42.

Recent reports about possible gas giant planets located in M42 have been drawing attention. 10 If confirmed, this shows that evolutionists cannot predict the minimum Jeans mass for gas clouds like M42 or what type of stellar mass distribution may form with any reliability. This makes me wonder about how reliable predictions for the minimum Jeans mass may be that are modelled using unobserved primordial star forming clouds and dark matter.


Pursuing the Firstborn Stars and a Better Cosmic Creation Model

Elusive detection of the universe’s firstborn stars has been a long-standing challenge toward developing a more detailed and better affirmed biblically predicted big bang creation model. 1 Astronomers call them Population III stars, and a failure to observe them has led some people to conclude that the big bang creation model has been falsified. For example, past president of the Institute for Creation Research, Henry Morris II, wrote,

The problem is that, out of the billions upon billions of stars in the observable universe, there do not seem to be any Type-3 Stars [Population III stars] at all. . . . It seems like we should see plenty of them if they ever existed, since all the other stars supposedly keep coming from them. 2

John Hartnett, Rod Bernitt, and Jonathan Sarfati of Creation Ministries International respectively wrote,

These original stars have never been observed, hence they were nothing more than hypothetical. . . . It [the Big Bang model] vitally needs t hose Population III stars or there is no story. 3 Their existence [of Population III stars] remains a matter of conjecture, not fact. 4 The total absence of these stars counts as a falsified prediction of Big Bang cosmology. 5

They base their critiques on the notion that in big bang cosmology the universe begins with only two elements, hydrogen and helium, and just a trace amount of lithium (with atomic weights of 1, 4, and 7, respectively). Therefore, the firstborn stars will possess no elements heavier than lithium. So far, the spectra of all observed stars reveal elements heavier than helium. (In a star’s spectrum astronomers see a star’s different colors of light and learn what a star is made of.)

Detection Difficulties
The irony in these critics’ assertions is that they overlooked the fact that the big bang creation model predicts that the spectra of the universe’s firstborn stars would be undetectable by present-day telescope power. Most big bang creation models predict that all Population III stars will be supergiant stars, stars larger than 20 times the mass of the Sun. Such stars will burn up in just several million years or less. Thus, they will be bright only in the very early history of the universe. Astronomers will see them only if they search for them at distances greater than 13.5 billion light-years away. No existing telescope has the power to measure the spectrum of a star at such a great distance.

A few big bang creation models predict that while most Population III stars will be supergiants, a small percentage may be stars 1–20 times the Sun’s mass, and a very tiny percentage may be as small as 0.8 times the Sun’s mass. Stars less than 0.8 times the Sun’s mass will burn for more than 13.5 billion years. Therefore, one or more of them might burn long enough to be close enough that astronomers can measure their spectra.

Such old Population III stars, however, will not be pristine. Their initial elemental makeup of only hydrogen, helium, and a trace amount of lithium will be contaminated by their atmospheres accreting small quantities of elements heavier than helium from the ashes of exploded supergiant Population III stars and ashes from the later-formed supergiant Population II stars. This contamination, though, will be minimized for old, low-mass Population III stars that have permanently resided in regions where the stellar density is very low.

New Spectral Measurements
Where spectral measurements reveal that this contamination is exceptionally low, specific details in the spectrum can reveal the precise source of the contamination and, therefore, positively determine whether or not the contaminated star is a true Population III star. A team of nine astronomers led by Rana Ezzeddine and Anna Frebel recently performed such measurements on the old star HE 1327-2326 to provide strong evidence that HE 1327-2326 is indeed a true Population III star that was contaminated more than 13 billion years ago by the nearby aspherical supernova explosion of a single high-mass Population III star. 6

A team of nineteen astronomers led by Anna Frebel discovered HE 1327-2326 in 2005. 7 They found it in the outer halo of our Milky Way Galaxy, a region where the density of stars is very low. HE 1327-2326’s mass is 0.8 times the Sun’s mass and its spectral features reveal it has completed its main sequence history of stellar burning. 8 Therefore, HE 1327-2326 likely is older than 13 billion years. In the discovery paper, Frebel’s team found that HE 1327-2326 had the lowest abundance of elements heavier than helium of any known star. Its ratio of iron to hydrogen measured to be only 1/250,000th of the Sun’s. 9

Today, HE 1327-2326 ranks as the star with the second lowest known abundance of elements heavier than helium. The recently discovered star SDSS J102915+172927 has an iron to hydrogen ratio less than 1/10,000,000th the Sun’s. 10

Unlike SDSS J102915+172927, HE 1327-2326 is not deficient in carbon. This feature led Ezzeddine and Frebel’s team to consider that HE 1327-2326 may be a low-mass Population III star that was externally enriched by the debris from a single high-mass Population III star that underwent an aspherical supernova explosion (see figure 1). To test their hypothesis, Ezzeddine and Frebel’s team used the Hubble Space Telescope to observe the ultraviolet spectrum (2,118–2,348 angstroms) of HE 1327-2326 for a total integration time of 22 hours and 20 minutes. For the first time ever, they got accurate measurements in this wavelength range of seven spectral lines of HE 1327-2326: one zinc line, five iron lines, and one silicon line.

Figure 1: Artist’s Rendition of an Aspherical Supernova Explosion.Image credit: NASA/CXC/M. Weiss

Observing Population III Stars
Armed with the new spectral measurements, Ezzeddine, Frebel, and their colleagues showed that the entire abundance pattern of HE 1327-2326 is explained by its being a Population III star that was blasted by one of the jets from a “rotation driven, high-energy (E = 5 x 10 51 erg) aspherical SNe [supernova eruption] with bipolar jets” 11 of a 25-solar-mass Population III star. Therefore, Ezzeddine and Frebel’s team established the existence of not just one, but two Population III stars.

Meanwhile, a team of Japanese astronomers has published two papers in which they demonstrate that astronomers may not need to wait for future super telescopes—like the James Webb Space Telescope or ground-based telescopes with mirror diameters larger than 30 meters (100 feet)—to directly detect high-mass Population III stars. The team shows that the near-infrared imaging capability of the 8.2-meter-diameter Subaru Telescope (see figure 2) combined with the natural magnification afforded by the gravitational lensing of intervening massive galaxy clusters may detect extremely distant massive Population III stars undergoing pair-instability supernova eruptions. 12

Figure 2: Subaru Telescope on Top of Mauna Kea in Hawaii.Image credit: Denys, Creative Commons Attribution

Already, the fact that Ezzeddine and Frebel’s team has established the existence of both high- and low-mass Population III stars will help astronomers develop a more detailed and specified big bang creation model. Such an advance will provide even stronger evidence for what the Bible had uniquely predicted about the universe thousands of years ago.


References

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Bonifacio, P., Limongi, M. & Chieffi, A. Nature 422, 834 (2003).

Umeda, H. & Nomoto, K. Nature 422, 871–873 (2003).

Schneider, R., Ferrara, A., Salvaterra, R., Omukai, K. & Bromm, V. Nature 422, 869–871 (2003).

Sneden, C. et al. Astrophys. J. (in the press) astro-ph/0303542 (2003).

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Wasserburg, G. J. & Qian, Y.-Z Astrophys. J. 529, L21–L24 (2000).


Texas astronomers revive idea for 'Ultimately Large Telescope' on the moon

Ultimately Large Telescope. Credit: University of Texas McDonald Observatory

A group of astronomers from The University of Texas at Austin has found that a telescope idea shelved by NASA a decade ago can solve a problem that no other telescope can: It would be able to study the first stars in the universe. The team, led by NASA Hubble Fellow Anna Schauer, will publish their results in an upcoming issue of The Astrophysical Journal.

"Throughout the history of astronomy, telescopes have become more powerful, allowing us to probe sources from successively earlier cosmic times—ever closer to the Big Bang," said professor and team member Volker Bromm, a theorist who has studied the first stars for decades. "The upcoming James Webb Space Telescope [JWST] will reach the time when galaxies first formed.

"But theory predicts that there was an even earlier time, when galaxies did not yet exist, but where individual stars first formed—the elusive Population III stars. This moment of 'very first light' is beyond the capabilities even of the powerful JWST, and instead needs an 'ultimate' telescope."

These first stars formed about 13 billion years ago. They are unique, born out of a mix of hydrogen and helium gasses, and likely tens or 100 times larger than the Sun. New calculations by Schauer show that a previously proposed facility, a liquid mirror telescope that would operate from the surface of the Moon, could study these stars. Proposed in 2008 by a team led by Roger Angel of The University of Arizona, this facility was called the Lunar Liquid-Mirror Telescope (LLMT).

NASA had done an analysis on this proposed facility a decade ago, but decided not to pursue the project. According to Niv Drory, a senior research scientist with UT Austin's McDonald Observatory, the supporting science on the earliest stars did not exist at that point. "This telescope is perfect for that problem," he said.

The proposed lunar liquid-mirror telescope, which Schauer has nicknamed the "Ultimately Large Telescope," would have a mirror 100 meters in diameter. It would operate autonomously from the lunar surface, receiving power from a solar power collection station on the Moon, and relaying data to satellite in lunar orbit.

Rather than coated glass, the telescope's mirror would be made of liquid, as it's lighter, and thus cheaper, to transport to the Moon. The telescope's mirror would be a spinning vat of liquid, topped by a metallic—and thus reflective —liquid. (Previous liquid mirror telescopes have used mercury.) The vat would spin continuously, to keep the surface of the liquid in the correct paraboloid shape to work as a mirror.

The telescope would be stationary, situated inside a crater at the Moon's north or south pole. To study the first stars, it would stare at the same patch of sky continuously, to collect as much light from them as possible.

"We live in a universe of stars," Bromm said. "It is a key question how star formation got going early in cosmic history. The emergence of the first stars marks a crucial transition in the history of the universe, when the primordial conditions set by the Big Bang gave way to an ever-increasing cosmic complexity, eventually bringing life to planets, life, and intelligent beings like us.

"This moment of first light lies beyond the capabilities of current or near-future telescopes. It is therefore important to think about the 'ultimate' telescope, one that is capable of directly observing those elusive first stars at the edge of time."

The team is proposing that the astronomical community revisit the shelved plan for a lunar liquid-mirror telescope, as a way to study these first stars in the universe.


Title: Gravitational waves from the remnants of the first stars in nuclear star clusters

pc). The merger rate density (MRD) peaks at $zsim 5-7$ with $sim 0.4-10 m yr^<-1> m Gpc^<-3>$, comparable to the MRDs found in the binary stellar evolution channel. Low-mass ($lesssim 10^<6> m M_$) NSCs formed at high redshifts ($zgtrsim 4.5$) host most ($gtrsim 90$%) of our mergers, which mainly consist of black holes (BHs) with masses $sim 40-85 m M_$, similar to the most massive BHs found in LIGO events. Particularly, our model can produce events like GW190521 involving BHs in the standard mass gap for pulsational pair-instability supernovae with a MRD $sim 0.01-0.09 m yr^<-1> Gpc^<-3>$ at $zsim 1$, consistent with that inferred by LIGO (within the 90% confidence interval). We predict a promising detection rate $sim 170-2700 m yr^<-1>$ for planned 3rd-generation GW detectors such as the Einstein Telescope that can reach $zsim 10$.


No, Today’s Stars Are Not The Same As Yesterday’s Stars

While the brightest stars dominate any astronomical image, they are far outnumbered by the fainter, . [+] lower-mass, cooler stars out there. In this region of the star cluster Terzan 5, a large number of stars are bound together in various configurations, but the large abundance of cooler, older, low-mass stars tells us that star formation mostly occurred long ago in this object.

When you look out at the Universe today, you’re not seeing it exactly as it is at one particular instant in time: now. Because of the fact that time is relative and light isn’t instantaneously fast — it can only move at the large, but not infinite, speed of light — we’re seeing things as they were when they emitted the light that only now is arriving. For an object like our Sun, the difference is cosmically minuscule: the Sun’s light arrives after a somewhat paltry journey of only 150 million km (93 million miles), which takes just a little over 8 minutes to complete.

But for the stars, star clusters, nebula, and galaxies we see across the Universe, because of their great cosmic distances, we’re seeing them as they were a much longer time ago. The closest stars are only a few light-years away, but for the objects that are millions or even billions of light-years distant, we’re seeing them as they were a significant fraction of the Universe’s history ago. The light that we receive from the most distant galaxy discovered so far — GN-z11 — was emitted when the Universe was just 407 million years old: 3% of its current age.

With NASA’s James Webb Space Telescope launching later this year, we’re poised to go back even farther. The stars from back then are fundamentally different from the stars we have today, and we’re about to find out exactly how.

As we're exploring more and more of the Universe, we're able to look farther away in space, which . [+] equates to farther back in time. The James Webb Space Telescope will take us to depths, directly, that our present-day observing facilities cannot match, with Webb's infrared eyes revealing the ultra-distant starlight that Hubble cannot hope to see.

The stars that exist today, for the most part, fall into two categories.

  1. There are stars similar to our Sun: with lots of elements other than hydrogen and helium in them, that were formed many billions of years after the Big Bang, and include lots of materials that must have been formed in previous generations of stars.
  2. There are stars that are fundamentally less evolved than our Sun: formed much closer back in time to the Big Bang than our own, with only a small amount of elements other than hydrogen and helium, whose material only includes a small amount that went through prior generations of stars.

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While that first type of star — what astronomers call “metal-rich” stars, since to an astronomer, any element on the periodic table that isn’t hydrogen or helium counts as a metal — can come in all different sizes, masses, and colors, the same isn’t true for that second type of star. The “metal-poor” stars in our Universe are overwhelmingly small, low in mass, and red in color.

Why are the metal-rich stars so diverse, but the metal-poor stars are all so similar to one another? The answer is simple: the metal-rich stars come in a wide variety of ages, but the metal-poor stars are all very, very old.

At a distance of 13,000 light-years, you won't be able to see Messier 71 with the same resolution as . [+] the Hubble Space Telescope, but this image should nevertheless give you a remarkable idea of how dense and brilliant the stars inside are. They are approximately 9 billion years old, spread out over a diameter of just 27 light-years, and much poorer in metals than stars like our Sun, which formed much more recently.

When we look out at the Universe and ask the questions, “where does it form stars,” we get a lot of different answers. You can have very small, isolated clouds of gas that cool and contract, eventually forming only a small number of stars. You can have larger clouds of gas that fragment into smaller clumps, producing a substantial cluster of stars in one location but only a small number elsewhere. Or you can have very large clouds of gas leading to intense periods of star formation, where thousands, hundreds of thousands, or even millions upon millions of stars are formed all at once.

Overwhelmingly, though, the majority of stars in the Universe are created during these major events of star-formation. It’s a little bit like the reverse of HBO’s Game of Thrones TV show: you might go for a few episodes where no one dies or only a few casualties occur here or there, but then there are these incredibly violent episodes where large numbers of people all die in one location. Well, star-formation is a bit like the opposite of that: it’s mostly quiet and steady, with a new star here or there, but the overwhelming majority of star-formation occurs in these bursts that create enormous numbers of new stars all at once, of all different varieties.

The open star cluster NGC 290, imaged by Hubble. These stars, imaged here, can only have the . [+] properties, elements, and planets (and potentially chances-for-life) that they do because of all the stars that died before their creation. This is a relatively young open cluster, as evidenced by the high-mass, bright blue stars that dominate its appearance, but there are hundreds of times as many lower-mass, fainter stars inside.

ESA & NASA, ACKNOWLEDGEMENT: DAVIDE DE MARTIN (ESA/HUBBLE) AND EDWARD W. OLSZEWSKI (UNIVERSITY OF ARIZONA, USA)

Today, whenever you make a large number of new stars all at once, here’s what happens.

  • The largest, most overdense regions of matter start to contract the fastest gravitation is a game of runaway growth, and whichever regions have the greatest amounts of mass collapse the earliest.
  • The contracting matter has to cool, radiating away the energy that’s gained from this gravitational contraction.
  • The richer in (astronomical) metals the gas is, the more efficient it is at radiating heat away, meaning that it’s easy for the gas to collapse and form new stars.
  • And how easy or hard it is for gas to collapse and form new stars determines what astronomers know as the “initial mass function,” which tells us what types, masses, colors, temperatures, and lifetimes of the stars that form will be.

Whenever you have a large star-forming region in the modern Universe, to the best of our knowledge, you always wind up with roughly the same sets of stars inside.

The classification system of stars by color and magnitude is very useful. By surveying our local . [+] region of the Universe, we find that only 5% of stars are as massive (or more) than our Sun is. It is thousands of times as luminous as the dimmest red dwarf star, but the most massive O-stars are millions of times as luminous as our Sun. About 20% of the total population of stars out there fall into the F, G, or K classes, but only

0.1% of stars are massive enough to eventually result in a core-collapse supernova.

Kieff/LucasVB of Wikimedia Commons / E. Siegel

On average, the mass of a typical star will be about 40% the mass of the Sun. Stars that are lower in mass than our Sun are going to be redder in color, less luminous in their intrinsic brightness, lower in temperature, and longer-lived (because the lower rate of fusion that occurs) relative to us. However, the overwhelming majority of the stars that are formed, somewhere around

80% of them, will be even less massive than the average star.

That leaves a lot of room for some very massive stars to form. About 15% of the stars that form will still be lower in mass than our Sun, but more massive than that

40% figure, leaving only 5% of all stars (by number) that are more massive than our Sun. But those stars are predominantly brighter, bluer, hotter, and also shorter-lived than our Sun is. The largest collection of them that we know about are found in a massive star-forming region in the Tarantula Nebula. Despite being located in the Large Magellanic Cloud, only the fourth largest galaxy in our Local Group, it’s the largest star-forming region around for almost 10 million light-years.

Hubble space telescope of the merging star clusters at the heart of the Tarantula Nebula, the . [+] largest star-forming region known in the local group. The hottest, bluest stars are over 200 times the mass of our Sun, although from our distance of 165,000 light-years away, we predominantly see the brightest, rarest stars the more common, lower mass ones are not clearly visible here.

NASA, ESA, and E. Sabbi (ESA/STScI) Acknowledgment: R. O'Connell (University of Virginia) and the Wide Field Camera 3 Science Oversight Committee

Even though the stars inside look like they’re predominantly blue and bright, this isn’t exactly the case. Instead, the stars that are bluest and brightest are the stars that are the most prominent and easily seen. The stars inside the Tarantula Nebula are already some

165,000 light-years away, and so it’s only the brightest ones that pop out as clearly visible to us. (It’s worth remembering that the closest star to our Sun, Proxima Centauri, was only discovered about 100 years ago. Even today, knowing exactly where it is, it takes a telescope about the diameter of your outstretched hand to see it at all.)

About 20% of the stars inside the Tarantula Nebula, like in any region that’s recently formed stars, are between about 40% and 800% the mass of our Sun. They will, typically, live for hundreds of millions to a few billion years, burn through the hydrogen in their cores, swell into red giants, fuse helium into carbon, and then expel their outer layers while their cores contract into white dwarfs. This process of stellar death forms what we call a planetary nebula, and is primarily responsible for the origin of many elements, like carbon and oxygen, that are essential to the biology and chemistry found on Earth.

The cluster RMC 136 (R136) in the Tarantula Nebula in the Large Magellanic Cloud, is home to the . [+] most massive stars known. R136a1, the greatest of them all, is over 250 times the mass of the Sun. While professional telescopes are ideal for teasing out high-resolution details such as these stars in the Tarantula Nebula, wide-field views are better with the types of long-exposure times only available to amateurs.

European Southern Observatory/P. Crowther/C.J. Evans

At the center of the Tarantula Nebula, however are the most massive individual stars we know of, with dozens of stars exceeding 50 solar masses, two heaping handfuls of stars over 100 solar masses, and the most massive one of all, R136a1, reaching an estimated mass of 260 Suns. The bright, blue stars burn through their fuel incredibly fast, shining many millions of times brighter than our own Sun. They also live for incredibly short timespans, burning through their core’s fuel in as little as 1-to-2 million years: one ten-thousandth the lifetime of a Sun-like star.

The stars that are more massive than about 8 solar masses, when they’re born, will eventually end their lives in a core-collapse supernova, which recycles the heavy elements that were forged inside the star — both during its life and during the supernova process — back into the interstellar medium, where it enriches the material that will be used for future generations of stars.

Supernova remnants (L) and planetary nebulae (R) are both ways for stars to recycle their burned, . [+] heavy elements back into the interstellar medium and the next generation of stars and planets. These processes are two ways that the heavy elements necessary for chemical-based life to arise are generated, and it's difficult (but not impossible) to imagine a Universe without them still giving rise to intelligent observers.

ESO / Very Large Telescope / FORS instrument & team (L) NASA, ESA, C.R. O’Dell (Vanderbilt), and D. Thompson (Large Binocular Telescope) (R)

This recycled material from supernovae is primarily responsible for the origin of a few dozen of the elements found in our Universe, but there are other ways that these stars contribute. In addition, the remnant at the core will be either a black hole or a neutron star, and both of those play a role in populating our Universe with the elements of the periodic table.

Neutron star mergers provide the majority of many of the heaviest elements in the Universe, including gold, platinum, tungsten, and even uranium. While our Sun might be a “singlet” star, don’t be fooled: about 50% of all stars exist in multi-star systems with two or more stars inside, and if two massive stars both become neutron stars, a merger is all but inevitable.

Meanwhile, black holes and neutron stars accelerate matter around them, creating high-energy particles known as cosmic rays. These cosmic rays collide with all sorts of particles, including some of the heavy elements that were created in earlier generations of stars. Through a cosmic process called spallation, where cosmic rays blast these heavy nuclei apart, some lighter nuclei are produced, including significant fractions of the lithium, beryllium, and boron (elements 3, 4, and 5) in the Universe.

When a high-energy cosmic particle strikes an atomic nucleus, it can split that nucleus apart in a . [+] process known as spallation. This is the overwhelming way that the Universe, once it reaches the age of stars, produces new lithium-6, beryllium and boron. Lithium-7, however, cannot be accounted for by this process.

Nicolle R. Fuller/NSF/IceCube

The thing is, these are the stars that have formed in the already-enriched Universe: the ones that formed recently or are still forming today. Earlier on, there were fewer generations of stars that lived-and-died, and that means that there were fewer heavy elements in the stars that formed long ago. Those metal-poor stars exist in great abundance in the outskirts of our galaxy: members of ancient structures known as globular clusters. But these are already many billions of years old all the massive stars in them already died long ago.

What are metal-poor stars like when they’re just born? And, going even farther back in time, what was the very first generation of stars like: the ones that were made of elements that only were created in the hot Big Bang?

In theory, they were far worse at “cooling” than today’s star-forming gas is, and so we expect that the earlier stars are:

compared to stars just forming today. We fully expect, with the James Webb Space Telescope launching later this year, that one of its prime science goals and discoveries will be to find, identify, image, and study these earliest populations of stars. If it succeeds, we might finally come to understand how good our theories of early star-formation are, and uncover just how massive these early, metal-free stars could get.

An illustration of CR7, the first galaxy detected that was thought to house Population III stars: . [+] the first stars ever formed in the Universe. It was later determined that these stars aren't pristine, after all, but part of a population of metal-poor stars. JWST will reveal actual images of this galaxy and others like it, capable of seeing through the neutral atoms permeating the Universe at these times.

What’s a certainty, however, is that the stars in the young Universe were significantly different than the stars that are just coming into existence today are. They were made of different materials the gas that collapsed to form them cooled at different rates the sizes, mass distributions, luminosities, lifetimes, and even the fates of these stars were likely very different from the stars we have today. Yet right now, we face the ultimate problem when it comes to learning about them: when we look out at the Universe around us, today, all we see are the survivors.

If we want to find the stars that once dominated the Universe, we have no other option: we have to look extremely far away, to the distant, ancient Universe. Billions upon billions of years ago, the Universe was filled with large amounts of newly formed, massive metal-poor stars, and at even earlier times, the first stars of all. With the advent of the James Webb Space Telescope, we fully expect these elusive stellar populations to not only be revealed to us, but revealed to us in detail. In the meantime, we can take solace in the fact that we understand how the Big Bang, stars, and stellar remnants gave rise to the elements in our Universe.

If we want to fill in the details we’re currently lacking, we have to look deeper, older, and fainter than ever before. The technology to take us there — NASA’s James Webb Space Telescope — is just months away from launch. If you haven’t understood why astronomers are so excited about this observatory up until now, perhaps “the origin of stars, leading to the origin of us” might help you feel some of that excitement for yourself.