Changing Planet

Smallest Galaxy Ever Discovered Bolsters Dark Matter Theory

This image shows a prediction for the distribution of thousands of dark matter clumps called halos within about 1 million light years of the Milky Way galaxy, The disk of the Milky Way sits within the white region at the center. The zoomed-in image is of Segue 2 lying within one of these halos.
Credit: Garrison-Kimmel, Bullock (UCI)


This week, astronomers announced that they have managed to weigh a minuscule galaxy that breaks the record for the smallest ever detected and may help shed light on mysterious dark matter.

With only 1000 stars huddled together, this galactic featherweight dubbed Segue 2 has just enough mass  for dark matter to act as a glue keeping it together, according to a new study published this week in The Astrophysical Journal. (See also Dark Matter Galaxy Detected)

“Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse,” said UC Irvine cosmologist and study co-author James Bullock in a statement.

Using the combined power of the twin 10 meter Keck telescopes perched on top of Mauna Kea in Hawaii, researchers were able to determine the weight of over a dozen of the most massive stars within this tiny galaxy. They were astonished to find that they were all ten times lighter than expected. A halo of surrounding dark matter–  the invisible material detectible only by the effects of its gravitational pull that scientists think makes up more than 80 percent of the mass in the universe – is what keeps Segue 2 together and qualifies it as a bonafide galaxy and not just a humdrum star cluster.

First glimpsed in 2009 by the Sloan Digital Sky Survey, Segue 2 turns out to be one of the faintest known galaxies too, shining with the power output of only 900 suns. To put that into perspective, our own Milky Way galaxy shines 20 billion times brighter. (Related Galaxy “Crumbs” Found in Milky Way—Proof of Recent Feeding)

Artist simulation of dark matter halo around the Milky Way galaxy.'s own backyard.  Credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)
Artist simulation of dark matter halo around the Milky Way galaxy.’s own backyard. Credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)

Small-fry galaxies like Segue 2 have been theorized to exist but have eluded detection until now. This discovery now bolsters our understanding of galactic formation across the universe and suggests that dark matter is indeed clumped into halos as predicted.

But co-author James Bullock and his team believe that tiny Segue 2 may in fact be just one of multitudes of tiny satellite galaxies buzzing around our Milky Way waiting to be discovered.

It could very well be only “a tip-of-the-iceberg observation, with perhaps thousands more very low-mass systems [dwarf galaxies] orbiting just beyond our ability to detect them,” he added. (See also Dying Galaxy Found Bleeding Out Into Space)


Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • Anthony Gordon

    Is it near Orion’s Belt ?

  • Tacoma Tarrer

    The author should proof-read his article before publishing it.

    “according to a new study publish [sic] this week”

    Who knows if his science is just as bad.

  • David Ames

    “They were astonishes to find that they were all ten times lighter than expected…:

    Let M be the weight expected. Theb M – (1M) = 0 is one time less than the weight expected and M – (10 M) = –9M is ten times less than the weight expected. When I took Freshman physics in 1964-5 negative weights were not discussed. Where can I update myself on this important topic?

  • Bongani Musawenkosi Mthembu

    Interesting find! I am sure there are more tiny Galaxies out there.

  • Christian Gonzalez

    “Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse.”

    It all depends on the size of the mouse.

  • Garry Crossan

    Look the way I see it, god made the earth and everything on it including mind altering substances like dmt, lsd, and such! herbal Cannabis and man has made such things illegal!! Medical cannabis cures cancer its been know since 1974 so in my eyes man greed for money has caused him to exploit the weak for profit. Its almost genacide!! the biggest pharmacuitcal companys dont want every man woman and child to have the access to the haeling

  • Garry Crossan

    The healing power of such plants and that is whats wrong with this world the rich and powerfull exploiting the week! Nikola tesla invented Alternating current and could pull free electricity from the atmosphere and send it around the world wirelessly and he said it should be free for everyone but the big wigs at the time who had invested in hydro from niagra falls would never let this happen they had big plans to keep us all hooked on the technology the would invent so sell a life style to our great gran parents

  • Nick Spanlopis

    In reply to David.

    You are arriving at your English wrong. If I am studying a rock and I expect it to be 10 tons and I measure it to determine its weight and find it to be 100 tons, I can then divide 10 tons by 100 tons and find that I predicted a tenth of its actual weight. Which means the rock was 10 times heavier than I predicted. Now reverse the numbers such that I predict 100 tons and find 10 tons, using the same process I find that the rock is 10 times lighter than I predicted.

    Sure there is math in there, but they weren’t describing a mathematical formula, they were using English precisely the way it is meant to be used, to communicate an understanding of what was found in an efficient form. They do that quite succinctly instead of a version of my long winded description above.

    In reply to Tacomma.

    Let the first person who has never published a typographical or grammatical error cast the first stone, it surely isn’t me.

  • RST5851

    Dark Matter holding atoms together forming matter from energy

    There are a number of theories on how the universe was created and how we came to exist, though this theory does not give the answer as to how it all began it does give a theory as to what dark matter is and how it affects the universe.
    Dark matter IS the fabric of space:
    I have tried to think of ways to explain this to be comprehendible for the average person out there:
    At some point in time pure energy is injected into the universe, science refers to this as The Big Bang, to give readers an easy understanding of what happens I will use condensing of gases to give you a batter image of what Dark matter is and what it is does to energy to form matter as time goes on, energy is condensed by dark matter, this crushes protons and neutrons together, as they are forced together, electrons form a field around the nucleus of the atom, atoms combine to form matter, imagine gases being condensed to form a liquid, this same type of process taking place to form matter from energy as dark matter condenses it .
    Energy does not belong with dark matter, this is like forcing water into a steal block that is sealed in a chamber with no room for anything, impossible to accomplish yet energy has found a way to enter into dark matter which created us and all matter throughout the universe and from my calculation it is still going on every day more energy is injected/forced into dark matter/space.

    Dark matter remains constant not increasing or decreasing in mass while energy continues to be injected into the universe which creates gravity waves, this is actually a wave created as dark matter and energy are squeezed together in the universe, this increases the condensing process reducing the size of atoms, I know some of you are thinking this could be measured but not as you may think due to everything being relative, as atoms are reduced in size all matter is also reduced/condensed, so let’s say the earth is reduced in size by this process as atoms are squeezed smaller and smaller your measuring equipment also becomes the same size, you would not notice it because (everything) has changed in size, the earth, moon and sun all reduce in size along with your ruler so everything is relative making measuring this only possible by the distance between stellar bodies.
    Measuring the process:
    Measure the atom being squeezed is only noticed as dark matter/space increases distances between stellar bodies, you will also notice the distance between the moon, earth and sun and other stellar bodies become further from one another and can be measured today.
    I would also like to have some research done on dinosaurs as I am wondering if the large sizes of mammals millions of years ago may have something to do with this process , just seems like it could be an interesting thing to research if my theory ends up holding up to the scientific community.

    The future of the universe:
    1. I theorize Energy will continue to fill the universe condensing the atoms until it reaches a critical point wherein another big bang will occur, this would increase the amount of dark matter by tearing the fabric of space/dark matter and doubling the space at the same time inflation of matter/atoms would occur allowing more energy to fill the new universe and these cycles continue over and over.

  • caleb byma

    very interisting i will take this into consideration and yes there are alot of other very very small galaxys

  • shainna

    is dark matter bad

  • brandon ginarte

    Is dark matter a theory because im doing a class project on scientific theories for 6th grade and dark matter really interests me. Hopefuly u can reply BTW the projects due in a week

  • george bush’s son

    i got the call of duty dark matter camo

  • mike hunt

    i find this very interested and my history teacher showed me this for fun very nice wa wa we wa

  • Liam Crocker

    wow this is cool to finally see a elephant smaller than a mouse.

  • Sonic


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