Astronomy

Number of stars & planets in Milky Way Galaxy?

Number of stars & planets in Milky Way Galaxy?


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Is there any specific numbers on stars & planets count on Milky Way Galaxy ?


A consensus number is that there roughly $10^{11}$ stars in our Galaxy (though this number is certainly uncertain by a factor of at least two, because it is based on extrapolating what we know about stellar populations in our vicinity). Most of these stars are of lower mass and are much less luminous than the Sun.

The number of planets is even more uncertain. It now seems probable that most stars like the Sun have at least one planet, but we really don't know that much about the diversity of planetary systems, how typical something like the solar system is, or how planetary systems might change as a function of position in the Galaxy. We also don't know that much about planetary systems around the dominant (by number) very low-mass stars. They certainly can have planetary systems, but the fraction that do is still a work in progress.


The number of stars and planets in the milky way can only be given in approximate values.There are about 100-400 billion stars and as of 2016 there are about 2097 planets discovered from 1337 planetary systems.


Astronomers Admit: We Were Wrong� Billion Habitable Earth-Like Planets In Our Galaxy Alone

Estimates by astronomers indicate that there could be more than 100 BILLION Earth-like worlds in the Milky Way that could be home to life. Think that’s a big number? According to astronomers, there are roughly 500 billion galaxies in the known universe, which means there are around 50,000,000,000,000,000,000,000 (5�) habitable planets. That’s of course if there’s just ONE universe.

Estimates by astronomers indicate that there could be more than 100 BILLION Earth-like worlds in the Milky Way that could be home to life. Think that’s a big number? According to astronomers, there are roughly 500 billion galaxies in the known universe, which means there are around 50,000,000,000,000,000,000,000 (5�) habitable planets. That’s of course if there’s just ONE universe.


Number of stars & planets in Milky Way Galaxy? - Astronomy

I am confused about the number of stars in our Milky Way galaxy. Some sources say that the Milky Way consists of 100 billion stars. Other say that the MASS of our galaxy is roughly 100 billion times the mass of the Sun. So because most of the galaxy mass is in the interstellar gaseous and dust nebulae there must be less than a 100 billion stars in it or the total mass must be greater. Which of these is correct? And did someone estimate the number of ACTUAL stars in our Galaxy?

Most of the mass in the galaxy is NOT in interstellar gaseous and dust nebulae. Most of the luminous matter is in stars and not nebulae. Now, the mass of the galaxy is mostly dominated by dark matter, which is something that is not detected by any telescope, or anything except through its gravity. But as far as the luminous matter goes, most of it is stars.

About the number of stars: People have studied the mass distribution of stars in the galaxy. Further, one also knows the amount of light put out by each type of star. So, by measuring the total amount of light in the galaxy (called luminosity), and knowing the mass, one can estimate the number of stars that are there in the galaxy. So, even though we cannot actually count the number of stars in the galaxy, we can estimate the number of stars in the galaxy as roughly 100 billion (100,000,000,000). It turns out that there are many more stars with mass less than the mass of the Sun than with mass more than the mass of the Sun. So, it all works out right.

This page updated June 27, 2015

About the Author

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.


'Rogue' planets could outnumber stars in the Milky Way, study suggests

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A newly published study suggests there could be more "rogue" planets, those that do not orbit a star, than there are stars in the Milky Way galaxy.

The research, published in the Astronomical Journal, notes the upcoming launch of the Nancy Grace Roman Space Telescope, slated to happen in 2025, could find billions, perhaps trillions of these objects.

“As our view of the universe has expanded, we’ve realized that our solar system may be unusual,” the study's lead author, Ohio State University graduate student Samson Johnson, said in a statement. “Roman will help us learn more about how we fit in the cosmic scheme of things by studying rogue planets.”

This illustration shows a rogue planet drifting through the galaxy alone. (NASA/JPL-Caltech/R. Hurt [Caltech-IPAC])

The telescope will continue to search narrow patches of sky for "free-floating planetary-mass objects (FFPs) [that] will be detected as isolated microlensing events with timescales shorter than a few days," the authors wrote in the study's abstract.

It could find objects with masses as small as Mars to those as large as gas giants with timescales as short as a few hours to "several tens of days," they added, thanks to the sensitivity of the lens.

“The microlensing signal from a rogue planet only lasts between a few hours and a couple of days and then is gone forever,” study co-author Matthew Penny added. “This makes them difficult to observe from Earth, even with multiple telescopes. Roman is a game-changer for rogue planet searches.”

So far, only a few rogue planets have been found, including two found a couple of years ago, according to a 2018 study.

Little is known about rogue planets, including what they are comprised of. NASA theorizes they could "form in isolation from clouds of gas and dust, similar to how stars grow," but that's just a theory.

It will be up to Roman to get a better idea of just how they form and how many there are. The researchers believe the mission could "detect hundreds of rogue planets," though they estimated the rogue planet count could be 10 times more precise than current estimates, which range from "tens of billions to trillions" in the Milky Way.

“The universe could be teeming with rogue planets and we wouldn’t even know it,” study co-author Scott Gaudi explained. “We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.”

More than 4,000 exoplanets have been discovered by NASA in total, approximately 50 of which were believed to potentially be habitable as of September 2018. They have the right size and the right orbit of their star to support surface water and, at least theoretically, to support life.


Size, Mass, and Distance

The Milky Way is part of the Local Group, holding the second title as the largest galaxy in it. Its stellar disk is approximately 100.000 light-years / 30 kpc in diameter.

It is approximately 1.000 light-years / 0.3 kpc thick. The Local Group is about 10 million light-years across, and the Andromeda galaxy is the most massive galaxy in it, The Milky Way is the second-most massive.

The Milky Way is almost 1.5 trillion times the mass of the Sun. If the Solar System were the size of a coin, the Milky Way would be the size of the contiguous United States.

Much of the mass seems to be dark matter, an unknown and invisible form of matter that interacts gravitationally with ordinary matter.

Milky Way’s mass has a radius of about 129.000 light-years. This suggests that about 90% of the mass is comprised of dark matter.


There may be 50 billion free-floating planets in our galaxy

Artist’s concept of rogue planet CFBDSIR J214947.2-040308.9. Image via ESO/L. Calçada/P. Delorme/Nick Risinger (skysurvey.org)/R. Saito/VVV Consortium.

Based on findings from space- and ground-based telescopes in recent years, astronomers now estimate there are billions of exoplanets – planets orbiting distant stars – in our galaxy alone. But what about planets that don’t orbit stars? How many rogue, or free-floating planets wander the depths of space unbound? Some have already been found, and earlier this year astronomers at the University of Leiden in the Netherlands announced results of their new study, suggesting there are some 50 billion free-floating planets in our Milky Way galaxy.

These astronomers’ results were published on February 14, 2019, in the peer-reviewed journal Astronomy and Astrophysics.

Only a dozen or so rogue planets have been discovered. How did these astronomers’ research determine there might be 50 billion more?

They ran computer simulations of 1,500 stars in the Trapezium star cluster, a well-known region of star formation located some 1,300 light-years away in the Orion Nebula, in the direction of our constellation Orion.

The simulation included 2,522 planets orbiting 500 stars within the Trapezium cluster and showed that 357 of them would become free-floating planets within the first 11 million years of their evolution. Simon Portegies Zwart, an astronomer at the University of Leiden, recently told Bruce Dorminey of Forbes:

Of these, 281 leave the cluster, others remain bound to the cluster as free-floating intra-cluster planets.

View of the Orion Nebula – a well-known region of star formation – via the Hubble Space Telescope. The Trapezium star cluster is the bright area just left of center. It contains about 2,000 known stars, but there may be more as well. It is a young open cluster where the stars are all roughly the same age. Image via NASA/ESA/Hubble Space Telescope.

So 281 of 2,522 newly born planets would leave their original star-forming cluster altogether, to roam the space between stars and star clusters, according to this computer simulation. The researchers then extrapolated those numbers to the rest of the galaxy, based on estimates of 200 billion stars in our galaxy. After all, the Trapezium star cluster is just one of thousands of known star clusters. All of the Milky Way’s stars are thought to have originated in vast star-forming clouds like those in the Orion Nebula, and to have started life in star clusters much like the Trapezium star cluster.

If, as calculated, about a quarter of the Milky Way’s stars have lost one or more planets, as many as 50 billion planets should be rogue or free-floating, in our galaxy alone!

Bound exoplanets likely outnumber stars in the galaxy our single sun has eight major planets, and we’ve now seen thousands of planets orbiting single stars in multiple-planet systems. The estimates for the total numbers of planets in our Milky Way – both bound to stars, and rogue – is staggering.

Just a few decades ago, it wasn’t yet known if any exoplanets existed. Now, current observations suggest there are hundreds of billions. Combine that with the billions of galaxies, and the implications are mind-blowing.

Closer view of the Trapezium star cluster in the Orion Nebula (bright stars near center of photo). Image via ESO/M.McCaughrean et al. (AIP).

Here is another question. Might any of those free-floating planets collide with other planets or with their stars? They can and do, according to these astronomers’ recent computer simulation. Zwart said in Forbes:

Collisions among planets and between planets and their host star are common. This happens in more than three percent of planetary systems.

Zwart also thinks that our own solar system might have lost one or two planets – probably less massive than Neptune – earlier in its youth. He said:

But who knows what happened very early on, when Jupiter and Saturn had just formed and the rocky planets just started to emerge.

Artist’s concept of exoplanet Kepler-186f. Most exoplanets – as might be assumed – orbit their own stars, but there may be billions more in our galaxy alone that do not. NASA/JPL-Caltech/T. Pyle.

The ejection of planets from their home planetary systems might be more common in denser star clusters (the Trapezium star cluster is considered a “looser” cluster), since more frequent encounters between stars in dense clusters will make the planetary systems unstable. But the study of the Trapezium cluster shows that planets leave their home systems in looser clusters as well.

Two of the dozen or so confirmed rogue planets so far were announced last year – OGLE-2012-BLG-1323 and OGLE-2017-BLG-0560. The first is estimated to have a mass between Earth and Neptune, while the other has a mass between Jupiter and a brown dwarf star.

Rogue planets are not easy to detect, but as astronomers learn more about them, they’ll be able to find more in the coming years. If this new study is any indication, there are many of them awaiting discovery.

Bottom line: The existence of 200 billion stars in our galaxy – and an even greater number of planets – is difficult enough to wrap our minds around. The idea of another 50 billion planets just floating around, not bound to any stars, is even more incredible. It might sound like science fiction, but, if astronomers at the University of Leiden in the Netherlands are right, these 50 billion rogue planets do exist.


17 Billion Earths of the Milky Way Explained (Infographic)

Astronomers studying data from the Kepler space telescope estimate that 17 percent of stars in the Milky Way galaxy have planets about the size of Earth. This means that about one in six stars has an Earth-size companionexoplanet. As there are about 100 billion stars in the galaxy, there are at least 17 billion Earth-size worlds in this galaxy alone.

Our own star possesses two Earth-size worlds. Earth itself, and the uninhabitable planet Venus, with its thick carbon dioxide atmosphere and a surface temperature of 870 degrees F (465 degrees C).

Large gas giant planets the size of Neptune or Jupiter are much less common than worlds the size of Earth.

The study finds that 17 percent of all stars probably have an exo-Earth (a planet 0.8 to 1.25 times the size of Earth) in an orbit of 85 or less Earth days.

About one in four stars have a super-Earth (1.25 to 2 times the size of Earth) in an orbit of 150 days or less. The same number of stars have a mini-Neptune (2 to 4 times the size of Earth in an orbit of 250 days or less.

Larger planets are much rarer. Three percent of stars have a large Neptune (4 to 6 times the size of Earth) and 5 percent have a gas giant (6-22 times the size of Earth) in an orbit of 400 days or less.

The research was done by the Harvard-Smithsonian Center for Astrophysics.


Scientists pinpoint how many planets in the Milky Way could host life

The Milky Way contains at least 100 billion planets. And scientists are hell-bent on finding which ones might harbor life.

Our galactic neighborhood may be bustling with other worlds, but a new study estimates that a mere 300 million of those 100 billion planets may have the right ingredients for life.

And some of them may be closer than we think.

The study, published on preprint server ArXiv and accepted for publication in The Astronomical Journal, provides perhaps the most reliable estimate of habitability in our galaxy to date

Previous guesses at how much of the Milky Way may be habitable have ranged between as much as 40 billion and as low as six billion planets.

But by using data from exoplanet hunting missions such as Kepler and Gaia, the researchers behind the new study claim that their estimate is much more accurate.

“This is the first time that all of the pieces have been put together to provide a reliable measurement of the number of potentially habitable planets in the galaxy,” Jeff Coughlin, an exoplanet researcher at the SETI Institute and Director of Kepler’s Science Office, and co-author of the new study, said in a statement.

The astronomers homed in on three main determinants for habitability. First, they estimated the number of exoplanets similar in size to Earth in the Milky Way — these are most likely to be rocky planets. Then, they looked at how many stars are similar in age and temperature to our Sun. Lastly, they considered whether the planets have the conditions necessary to support liquid water, a critical ingredient for life.

Older studies only considered the distance of a planet from its host star to calculate habitability — a gross measure, the new study suggests. Instead, this research also takes into account how much light a planet would receive from its star based on more than mere distance alone. NASA's Kepler mission zoomed in on stars to see if there are planets orbiting within their habitable zone. Meanwhile, the European Space Agency's Gaia mission measured the positions, distances, and motions of stars to get a more definitive estimate of how much light — and thus, heat — they bestow on their planets.

The study found that there could be 300 million habitable planets in the Milky Way. Some are just 30 light years from the Sun, the data suggest.

Scientists have confirmed the existence of more than 4,000 exoplanets, although 3,000 more suspected exoplanets are awaiting confirmation. Some of these planets have shown signs of potential habitability, but whether they do host life will be extremely difficult to determine.

“Knowing how common different kinds of planets are is extremely valuable for the design of upcoming exoplanet-finding missions,” Michelle Kunimoto, member of the Transiting Exoplanet Survey Satellite team at the Massachusetts Institute of Technology and co-author of the new study, said in a statement. “Surveys aimed at small, potentially habitable planets around Sun-like stars will depend on results like these to maximize their chance of success.”


Milky Way has more planets than stars

The more astronomers look for other worlds, the more they find that it is a crowded and crazy cosmos. They think planets easily outnumber stars in our galaxy and they are finding them in the strangest of places.

And they have only begun to count.

Three studies released Wednesday, in the journal Nature and at the American Astronomical Society's conference in Austin, Texas, demonstrate an extrasolar real estate boom. One study shows that in our Milky Way, most stars have planets. And since there are a lot of stars in our galaxy, about 100 billion, that means a lot of planets.

"We're finding an exciting potpourri of things we didn't even think could exist," said Harvard University astronomer Lisa Kaltenegger, including planets that mirror Luke Skywalker's home planet in Star Wars, with twin suns and a mini-star system with a dwarf sun and shrunken planets.

"We're awash in planets where 17 years ago we weren't even sure there were planets" outside our solar system, said Kaltenegger, who wasn't involved in the new research.

Astronomers are finding other worlds using three different techniques and peering through telescopes in space and on the ground. Confirmed planets outside our solar system, called exoplanets, now number well over 700, but still-to-be-confirmed ones are in the thousands.

NASA's new Kepler planet-hunting telescope in space is discovering exoplanets that are in a zone friendly to life and detecting planets as small as Earth or even tinier. That is moving the field of looking for some kind of life outside Earth from science fiction toward plain science.

One study in Nature this week figures that the Milky Way averages at least 1.6 large planets per star. And that is likely a dramatic underestimate.

That study is based on only one intricate and time-consuming method of planet hunting that uses several South American, African and Australian telescopes. Astronomers look for increases in brightness of distant stars that indicate planets between Earth and that pulsating star. That technique usually finds only bigger planets and is good at finding those further away from their stars, sort of like our Saturn or Uranus.

Kepler and a different ground-based telescope technique are finding planets closer to their stars. Putting those methods together, the number of worlds in our galaxy is probably much closer to two or more planets per star, said the Nature study author Arnaud Cassan of the Astrophysical Institute in Paris.

Dan Werthimer, chief scientist at the University of California Berkeley's search for extraterrestrial intelligence program and who wasn't part of the studies, was thrilled: "It's great to know that there are planets out there that we can point our telescopes at."

Kepler also found three rocky planets smaller than Earth that are circling a dwarf star that itself is only a bit bigger than Jupiter. They are so close to their small star that they are too hot for life.

"It's like you took your shrink ray gun and you set it to seven times smaller and zap the planetary system," said California Institute of Technology astronomer John Johnson, co-author of the study presented Wednesday at the astronomy conference. Because it is so hard to see these size planets, they must be pretty plentiful, Johnson said. "It's kind of like cockroaches. If you see one, then there are dozens hiding."

It's not just the number or size of planets, but where they are found. Scientists once thought systems with two stars were just too chaotic to have planets nearby. But so far, astronomers have found three different systems where planets have two suns, something that a few years ago seemed like purely Star Wars movie magic.

"Nature must like to form planets because it's forming them in places that are kind of difficult to do," said San Diego State University astronomy professor William Welsh, who wrote a study about planets with two stars that's also published in the journal Nature.

The gravity of two stars makes the area near them unstable, Welsh said. So astronomers thought that if a planet formed in that area, it would be torn apart.

Late last year, Kepler telescope found one system with two stars. It was considered a freak. Then Welsh used Kepler to find two more. Now Welsh figures such planetary systems, while not common, are not rare either.

"It just feels like it's inevitable that Kepler is going to come up with a habitable Earth-sized planet in the next couple of years," Caltech's Johnson said.


New Estimates Say 6 Billion Earth-Like Planets Exist in Our Milky Way Galaxy

Plenty to colonize. if humanity could ever get there.

Canadian astronomers have estimated that there are as many as 6 billion Earth-like planets in our own galaxy—some of which could harbor alien life.

The exciting new findings, which were published in The Astronomical Journal, were extrapolated from data from NASA’s now-retired Kepler telescope, which spent nearly a decade in space looking for exoplanets all across the galaxy.

To be considered an Earth-like planet, the world must be rocky, roughly the same size as Earth and should orbit in the habitable zone of a sun-like (G-type) star. At such a distance from a star, the planet might possess water in liquid form, which could potentially provide a habitable environment.

“My calculations place an upper limit of 0.18 Earth-like planets per G-type star,” the study’s co-author Michelle Kunimoto, a researcher at University of British Columbia (UBC), said in a release.

“Estimating how common different kinds of planets are around different stars can provide important constraints on planet formation and evolution theories, and help optimize future missions dedicated to finding exoplanets.”

According to UBC astronomer Jaymie Matthews, our Milky Way galaxy “has as many as 400 billion stars, with 7% of them being G-type.”

Some previous estimates regarding the number of Earth-like planets started as low as 0.02 potentially habitable worlds per sun-like star.

Generally, smaller distant worlds that resemble Earth are missed more often by telescopes and planet hunters, which means that a planet catalog represents only a small subset of the planets that are actually in orbit around the stars that are being studied.

The UBC team tapped into a technique known as “forward modeling” to overcome such obstacles.

“I started by simulating the full population of exoplanets around the stars Kepler searched,” Kunimoto said.

“I marked each planet as ‘detected’ or ‘missed’ depending on how likely it was my planet search algorithm would have found them. Then, I compared the detected planets to my actual catalog of planets. If the simulation produced a close match, then the initial population was likely a good representation of the actual population of planets orbiting those stars.”

Previously, Kunimoto searched archival data from 200,000 stars of the Kepler mission to discover 17 new exoplanets, in addition to recovering thousands of already-known planets.

These new findings come in the same week that astronomers at the University of Nottingham estimated that there could be 36 intelligent civilizations in our galaxy.

Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek and Arirang TV. Follow or contact him on LinkedIn.