For the First Time, Scientists May Detect Dark Matter in Nearby Galaxy

November 24, 2015 | Joanne Kennell

Accelerated Expansion of the Universe after Big Bang
Photo credit: Alex Mittelmann, Coldcreation/Wikipedia (CC BY-SA 3.0)

Will this nearby galaxy solve the mysteries of dark energy and matter?

The weird thing about dark energy and dark matter is that we know how much there is because of how it affects the Universe’s expansion, but it has never been directly observed — not once.  It is a complete mystery.                     

In the early 1990s, scientists were certain that the effect of gravity on the universe was to slow down its expansions over time.  Boy, were they in for a shock.  In 1998, scientists discovered that the universe was expanding faster than it had in the past by measuring a distant supernova using the Hubble Space Telescope.  Wait, so the universe is expanding faster… How is this possible?

Scientists are still not sure why our universe is accelerating as it expands, but there are currently three possible explanations:

  1. The “cosmological constant” proposed in an older version of Einstein’s Theory of Relativity is real

  2. There is an energy-fluid that fills space

  3. There is something wrong with Einstein’s Theory of Gravity

If the third was found to be true, everything we know about the laws of gravity today could be wrong.  Although the answer to what causes the expansion is not known, scientists have named the solution “dark energy.”

Surprisingly, a whopping 68 percent of the universe is dark energy, 27 percent is dark matter, and the remaining five percent is made up of everything else that has been observed on Earth and in the universe.  That is mind-boggling.

Scientists do not really know what dark energy is, other than that it is there.  Dark matter, on the other hand, scientists know more about.  First of all, dark matter is well… dark.  It is not in the form of dark clouds made up of particles known as baryons, nor is it antimatter, and it is also not black holes.  The leading theories on what dark matter could be are that it is either made up of axions or supersymmetric WIMPS (Weakly Interacting Massive Particles).

The answers to these mysteries could be just around the corner.  Astronomers may have discovered that a small, nearby galaxy, Triangulum II, is made up of mostly dark matter.  The mass of this galaxy, measured by Evan Kirby, Assistant Professor of Astronomy at the California Institute of Technology, cannot be accounted for by just its stars.  Scientists say the ratio of dark matter to visible matter is the highest in any known galaxy.

Luckily, this galaxy is right at the edge of our Milky Way, making it a leading candidate to directly measure dark matter signatures.  But Triangulum II is tough to observe because it has so few stars — only 1000, compared to our Milky Way’s three billion.  Of these 1000 stars, only six were bright enough to be observed by the Keck telescope in Hawaii — one of the largest telescopes used today.

The following statement from CalTech explains how this galaxy can be used to detect dark matter:

“While current theories predict that dark matter is producing gamma rays almost everywhere in the universe, detecting these particular signals among other galactic noises, like gamma rays emitted from pulsars, is a challenge.

Triangulum II, on the other hand, is a very quiet galaxy. It lacks the gas and other material necessary to form stars, so it isn’t forming new stars—astronomers call it “dead.” Any gamma ray signals coming from colliding dark matter particles would theoretically be clearly visible.”

It is still not confirmed if what Kirby measured was the actual total mass of the galaxy, and another group of researchers from the University of Strasbourg suggested that this galaxy was being pulled apart or “tidally disrupted” by the gravity of our Milky Way.

"My next steps are to make measurements to confirm the other group's findings," said Kirby.


Read Next: What is Dark Energy and How Do We Know It Exists?

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