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Its often said that the number of grains of sand on Earth equals the number of stars in the Universe. Well it looks like a recent study by astronomers working at the Keck Observatory in Hawaii have found that its more like three times the number of grains of sand on Earth! Working with some of the most sophisticated equipment available, astronomers from Yale University have been counting the number of dim red dwarf stars in nearby galaxies which has led to a dramatic rethink of the number of stars in the Universe.
Red dwarfs are small, faint stars compared to most others and until now, have not been detected in nearby galaxies. Pieter van Dokkum and his team from Yale University studied eight massive elliptical galaxies between 50 and 300 million lights years from us and discovered that these tiny stars are much more bountiful than first thought. “No one knew how many of these stars there were,” said Van Dokkum. “Different theoretical models predicted a wide range of possibilities, so this answers a long standing question about just how abundant these stars are.”
For years astronomers have assumed that the number of red dwarfs in any galaxy was in the same proportion that we find here in the Milky Way but surprisingly the study revealed there are about 20 times more in the target galaxies. According to Charlie Conroy of the Harvard-Smithsonian Center who also worked on the project, “not only does this affect our understanding of the number of stars in the Universe but the discovery could have a major impact on our understanding of galaxy formation and evolution.” Knowing that there are now more stars than previously thought, this lowers the amount of dark matter (a mysterious substance that cannot be directly observed but its presence inferred from its gravitational influence) needed to explain the observed gravitational influence on surrounding space.
Not only has the discovery affected the amount of dark matter we expect to find but it also changes the quantity of planets that may exist in the Universe. Planets have recently been discovered orbiting around other red dwarf stars such as the system orbiting around Gliese 581, one which may harbour life. Now that we know there are a significantly higher number of red dwarfs in the Universe, the potential number of planets in the Universe has increased too. Van Dookum explains “There are possibly trillions of Earth’s orbiting these stars, since the red dwarfs they have discovered are typically more than 10 billion years old, so have been around long enough for complex life to evolve, its one reason why people are interested in this type of star.”
It seems then that this discovery, which on the face of it seems quite humdrum, actually has far reaching consequences that not only affect our view of the number of stars in the Universe but has dramatically changed our understanding of the distribution of matter in the Universe and the number of planets that may harbour intelligent life.
The new findings appear in the Dec. 1st online issue of the journal Nature.
Source: from the Harvard Smithsonian Center for Astrophysics.
Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro
Any links available to the press release or relevant journal?
I have always felt that dark matter was a hoax. If you can not account for something, well it must be hidden!!!
That’s nice, Harry, but none of the competing theories to Dark Matter hold up to scrutiny, while DM does. Occam’s Razor and all that. Besides, tripling the number of red dwarf stars isn’t likely to make that much of a dent in the matter/dark matter ratio.
http://keckobservatory.org/news/discovery_triples_total_number_of_stars_in_universe/
It might make a little difference. I’m also betting that there are [i]lots[/i] more brown dwarfs out there, at least twice as many as red dwarfs, maybe way more than that.
I’m a little skeptical that there could be trillions of earth-like planets around red dwarfs, as it would depend on the metal content available when these stars formed – especially the really really old ones.
Thanks for the link, Aqua. I was trying to find more info on the Dark Matter implications mentioned in the post. I found this info over at Yahoo! Canada News:
“Using the Keck telescope in Hawaii, van Dokkum and a colleague gazed into eight other distant, but elliptical, galaxies and looked at their hard-to-differentiate light signatures. The scientists calculated that elliptical galaxies have more of those dwarf stars. A lot more.
“We’re seeing 10 or 20 times more stars than we expected,” van Dokkum said. By his calculations, that triples the number of estimated stars from 100 sextillion to 300 sextillion.
For the past month, astronomers have been buzzing about van Dokkum’s findings, and many aren’t too happy about it, said astronomer Richard Ellis of the California Institute of Technology.
Van Dokkum’s paper challenges the assumption of “a more orderly universe” and gives credence to “the idea that the universe is more complicated than we think,” Ellis said. “It’s a little alarmist.”
Ellis said it is too early to tell if van Dokkum is right or wrong, but it is shaking up the field “like a cat among pigeons.”
Van Dokkum agreed, saying, “Frankly, it’s a big pain.”
Ellis said the new study does make sense. Its biggest weakness might be its assumption that the chemical composition of dwarf stars is the same in elliptical galaxies as in the Milky Way. That might be wrong, Ellis said. Even if it is, it would mean there are only five times more red dwarf stars in elliptical galaxies than scientists previously thought, instead of 10 or 20, van Dokkum said.”
Hmmm. Mebbe there’s a preprint of this paper out there. I’ll see what I can find.
@Harry,
I think Dark Gnat and QEV have the right idea. This is not a DM killer.
Found a preprint of the paper here: http://arxiv.org/PS_cache/arxiv/pdf/1009/1009.5992v1.pdf
Ron Cowen has a more detailed write-up @Science News: http://www.sciencenews.org/index/generic/activity/view/id/66894/title/Its_really_full_of_stars
As noted by Richard Ellis in my previous post, assumptions made on the makeup of dwarf stars in various types of galaxies may be problematic.
This does not do away with dark matter. Galaxies are surrounded by something that has no luminous properties which results in the non-Keplerian motion of stars. That can’t be accounted for by red or brown dwarf stars. Einstein microlensing measurements also put an upper bound on the number of brown dwarfs that is not sufficient to account for dark matter. Given that over half the luminous mass of galaxies is gas and dust, this result probably adjusts dark matter from 78% of a galaxy mass to maybe 70%. This is a significant result, but other data such as the Bullet galaxy collision with Einstein lensing clearly show nonluminous matter or dark matter does exist.
LC
Not to mention that these “new” red dwarfs are, of course, still part of the universe’s baryonic component, which is clearly overshadowed by dark matter according to cosmological observations.
I can’t find the article on Nature. Ever since they remodeled the site, it’s been extremely hard to find online publications.
It is only my point of view, but I would say, that this discovery is only the first of this kind – I mean, that there is so much of things we didn’t see in the Universe, next could be brown dwarfs or anything else. It is true, that this doesn’t remove the need for something like dark matter, but it decreases the amount of it needed to explain the movement of the stars. And if more discoveries follow, this amount could get even smaller and smaller.
After that it could be maybe easier to fill this gap by other alternative theories, like MOND or similiar.
If I had to guess, I would say it is the rotational properties of the different kinds of galaxies that determines the amount of stars of different sizes. The current favoured stellar formation model is that stars form from clouds of gas that collapse under their own gravity. Though the collapse would normally stop (or at least slow right down) before anything interesting happens due to hydrostatic equilibrium, turbulent motions lead to the chance appearance of blobs of gas dense enough to collapse further and form stars. Thus each giant cloud forms lots of stars, seeded by turbulent motion.
Something needs to drive the turbulence, or it dies out very, very quickly, and I’m not sure what that is- but I’m guessing that the various motions of things within the galaxy have an influence. Intuitively I would expect in a spiral galaxy, which has nice orderly rotation, that large-scale turbulence would be imparted to the cloud. Large disturbances -> large knots of turbulence -> massive stars. Contrariwise, in an elliptical galaxy where the stars and other things in it move in more random orbits, I would intuitively expect that smaller scale, frothy disturbances would be imparted to the could. Lots of small disturbances -> lots of small knots -> lots of small stars.
The is, of course, the problem that many ellipticals seem to be formed from the merger of spirals. Shouldn’t the resulting elliptical have the same stellar mass properties as the spirals it’s made from? I don’t think this is necessarily a fatal objection if mergers cause more star formation since such events are fairly disorderly anyway.
Of course, I may be totally off base here.
I have written about this several times here. The Poisson equation gives very different gravitational orbits for matter concentrated in a central region and orbits outside and for orbits within some distribution of matter. The non-Keplerian orbits of stars in a galaxy indicate the existence of a ball of invisible material around the galaxy. The presence of additional red dwarf stars, even if they double or triple the number of stars in a galaxy has a comparatively minor influence on our estimate of how much matter is dark matter.
LC
Let me try and paraphrase LC a bit…
We are out on the arms of a spiral galaxy. We orbit the galaxy once in about a quarter of a billion years.
If most of the mass lay at the middle of the galaxy, then we would expect the inner stars to orbit more quickly, like the planets do in the solar system. There, the time taken to go around the sun varies as the orbital radius to the one-and-a half power. If you are twice as far out, then you will take just under three times as long to do an orbit. Well, the mass of our galaxy does not all lie at the middle, but we can correct for that.
So far so good. If our galaxy was originally some irregular smudge, then it will get stirred into a spiral in a galactic year or so, because the bits on the outside go around more slowly than the bits in the middle. But the Earth is over four and a half billion years old, which is eighteen or so galactic years. That ought to have stirred the spiral into an almost smooth disc. Instead, it seems as though the middle and the outside of the galaxies rotate at almost the same rate. They are turning almost as though they were solid, rigid objects.
What explanations are there for this? Is space rigid? Is space viscous over very long distances? The least mad explanation is that there is some significant extra mass around the outside of a galaxy that we cannot see.
Can red dwarfs fit this missing mass? It is difficult to see how. The paper suggests there are lots more red dwarfs in elliptical galaxies. To explain our galaxy spiral, we need to add extra red dwarfs to a spiral galaxy. They are not very massive, so we would have to add a lot of them. We would have to add them right on the edges of our galaxy, where we ought to be able to see them…
No extra red dwarves there, I’m afraid, so we are still stuck with dark matter. I am no fan of the stuff, but I haven’t got a better explanation. But I am sure we will someday soon.
Kepler’s law can be derived from Newton’s law
m(omega^2)r = -GMm/r^2, omega = angular velocity
which gives us the rule of periodicity squared is proportional to orbital radius cubed. If the motion of stars was entirely due to dark matter evenly distributed the force law is ma = -kr, identical to the spring force, which gives a periodicity = constant. That is the case of a rotation similar to a solid disk, where the velocity increases with radius. The observed rotation is more of a constant velocity outside of the galaxy bulge. So the velocity v = omega*r and so the angular velocity is omega ~ 1/r, and not constant. Newton’s second law F = ma = m(omega^2)r gives us that the force has a variation with radius as
m(omega^2)r ~ mv^2/r = F
where here the v is constant and the force varies as 1/r, instead of as 1/r^2 with central force Newtonian gravity or as F ~ r with the spring force law one predicts with the a uniform distribution of matter.
The velocity of stars in or near the bulge becomes more Kepler-like, and velocities of stars in the disk suggest a sort of hybrid between Keplerian and spring force motion. The bulge, its central distribution of matter and the matter interior to any orbit in the disk is sufficient to induce departures from the spring force law. This is one of the motivations for the MOND idea, but that really is not much more than a phenomenological idea IMO.
LC
I think the important part here is that this newly detected additional population of red stars _are_ part of the dark matter scientists are searching for, but its much to small part to explain away anything of dark matter as a whole. Neither would an excess of brown dwarfs be able to eplain away all the dark matter.
I really like Mr. Crowell’s designation of “nonluminous matter”. This seems like a more precise description of where we are currently at with this theory. Noone would deny that there is unseen mass out there. How much though…? Could it simply be that over time more discoveries like the one in this article will gradually chip away at the overall percentage of DM until we are left with something far more workable?
Ok, who’s gonna run the Drake equation with the new numbers? This would mean that the theoretical amount of find civilizations are to be multiplied by at least three times. This seems more relevant than NASA’s recent findings.
An why does our galaxy seem to be low on these dwarf stars? Are we sure we identified them properly?
The increase in the numbers of red dwarf stars might increase the number of biologically active planets. This is of course depending on whether red dwarf stars are really able to support bio-planets. There are a fair number of these stars, and account for about 50% of all stars in the Milky Way galaxy. This seems to be low, based on this article, when compared to other galaxies. So we might be able to get signatures of life around a few red dwarf stars in our galaxy or within 1000ly or so. When it comes to alien civilizations, I have grim doubts that we will ever make any sort of contact. I suspect that intelligent life that is comparable to human capabilities is a very rare commodity in the universe.
LC
What is known about the chances of red and brown dwarfs to support life? It’s facinating that life on a planet hosted by a dwarf star can be much older than elsewhere in bigger star systems like ours. Also, their star will shine for a much longer time. Since they can’t be older than the age of the universe, this means at this point in time life elsewhere is three times older at most. When you compare the maximum age difference of lifeforms hosted by dwarfs and bigger stars at anytime in the far future, this number will be much bigger. This seems to me that life on Earth is amongst one of the first lifeforms ever to exist in the universe. This would explain quite a few things, including the lack of alien visitors and our relative stupidity.