GALAXY WITHOUT DARK MATTER CHALLENGES CURRENT SCIENCE

Amateur stargazers like me find it hard to locate galaxies in the night sky. I guess we shouldn’t be too hard on ourselves, since the existence of other galaxies only came to light about 100 years ago.

That’s when astronomer Edwin Hubble realized the Andromeda Galaxy was unimaginably far away. That meant there were other galaxies far beyond the Milky Way.

On a clear, dark Autumn night far from the light pollution of cities, we can spot our nearest galactic neighbour by looking toward the constellation Andromeda, and we don’t need binoculars or a telescope. If we’re ambitious, we can also find another galaxy called M33 in the nearby constellation Triangulum.

What Seemed Like Settled Science Had to be Reconsidered

Finding out about these other galaxies upset cosmologists’ apple cart in the early 20th century. What seemed like settled science had to be reconsidered from several perspectives.

One puzzle began with the Swiss astronomer Fritz Zwicky in the 1930s. He was studying the Coma Cluster of galaxies, comparing their apparent mass with their shape and motion.

He tried to calculate the masses of those galaxies based on the number of stars he could identify. Then, he tried to estimate the gravity at work in those galaxies based on how they moved.

“Unexplained Discrepancy Called Missing Matter”

Zwicky discovered that the mass he came up with couldn’t account for the gravitational motion he saw. He called this unexplained discrepancy “missing matter” at first, and then settled on the term “dark matter.”

This discrepancy wasn’t something small that might have resulted from measurement error or some sort of miscalculation. Zwicky found at least 400 times more gravity at work in the Coma system than the starlight he saw could account for.

Scientists still see this odd discrepancy between galaxies’ gravitational motion and their stars’ apparent mass. Zwicky’s figure of 400 times now seems on the high side, but until recently, scientists believed galaxies without dark matter were impossible .

Professor Comeron Studies Nearby Galaxy Evolution

Dr. Sebastien Comeron is an astronomer at the University of La Laguna in Spain, and at the Canary Islands Astrophysical Institute. He studies nearby galaxies to learn more about how they evolve.

These days, leads a team that studies the thick discs astronomers see when they view local galaxies edge-on. He likes to call his work “galactic archeology.”

Professor Comeron is the lead author of a study the journal Astronomy and Astrophysics published this week. It involves observations the researchers made of a galaxy called NGC 1277.

Very Old Galaxy in the Perseus Cluster

It’s a very old galaxy that’s part of a cluster in the constellation Perseus. It formed very quickly about 12 billion years ago, when the universe was only about one-sixth of its current age.

NGC 1277 is quite compact, it has an unusually massive central bulge, and it lacks prominent spiral arms. So, astronomers call it a lenticular galaxy rather than a spiral galaxy like our Milky Way.

Cosmologists also consider galaxies like NGC 1277 “relic galaxies” because of their age and also because they don’t seem to interact with neighbouring galaxies. They’re rare, and they provide insights into the early history of our universe.d

“Helping Us Understand How First Galaxies Formed”

“The importance of relic galaxies in helping us to understand how the first galaxies formed was the reason we decided to observe NGC 1277 with an integral field spectrograph,” Professor Comeron explained. “From the spectra, we made kinematic maps which enabled us to work out the distribution of mass within the galaxy out to a radius of some 20,000 light years.”

As if NGC 1277 wasn’t odd enough, the researchers have discovered something even more astonishing. Unlike other galaxies, NGC 1277 appears to be a massive galaxy without dark matter.

 “This result does not fit in with the currently accepted cosmological models, which include dark matter,” Professor Comeron said. Most scientists support a theory that the missing matter is a mysterious substance that has mass but doesn’t interact with light, so we never see dark matter, only its gravitational effects.

Less Than Five Percent Dark Matter, Maybe None

When Professor Comeron and his colleagues examined the shape of NGC 1277, the only gravity they saw came from its stars. Unlike other galaxies, NGC 1277 seems to be less than five percent dark matter, and it could be a massive galaxy without any dark matter at all.

Team member Dr. Ignacio Trujillo added, ”This discrepancy between the observations and what we would expect is a puzzle, and maybe even a challenge for the standard model.” His colleague Dr. Anna Ferre-Mateu outlined two potential explanations for a galaxy without dark matter.

“One is that the gravitational interaction with the surrounding medium within the galaxy cluster in which this galaxy is situated has stripped out the dark matter,” Professor Ferre-Mateu pointed out. “The other is that the dark matter was driven out of the system when the galaxy formed by the merging of protogalactic fragments, which gave rise to the relic galaxy”.

“Massive Galaxy Without Dark Matter Remains a Puzzle”

The scientists aren’t completely convinced by either explanation. “The puzzle of how a massive galaxy can form without dark matter remains a puzzle,” Professor Comeron said.

Despite our growing scientific knowledge and expertise, the universe is always full of surprises. Since scientists believe that dark matter makes up something like 27% of our universe, explaining what's behind it is vital to uncovering the new story humanity needs about our universe and our place within it.

And Another Thing…

This new “riddle wrapped in a mystery” of a galaxy without dark matter is also humbling. That’s a good thing, because we humans could use a little humanity, given the way we look after our own planet.

The team’s next step is to make more detailed observations using the WEAVE instrument on the William Hershel Telescope at the Roque de los Muchachos Observatory in the Canary Islands. They’re  hoping to rule out some of the fringe explanations for their apparent galaxy without dark matter, especially some that seem to defy the law of gravity.

We always have more to learn if we dare to know.

Learn more:

The puzzle of the galaxy with no dark matter

The massive relic galaxy NGC 1277 is dark matter deficient

Galaxies Without Dark Matter Might Form From Collisions

Massive Early Galaxies Discovery Could Be 'Universe Breaker'

Dark Energy Measured More Precisely Than Ever