Nav: Home

Dark matter is a no show in ghostly galaxy

March 28, 2018

Galaxies and dark matter go hand in hand; you typically don't find one without the other. So when researchers uncovered a galaxy, known as NGC1052-DF2, that is almost completely devoid of the stuff, they were shocked.

"Finding a galaxy without dark matter is unexpected because this invisible, mysterious substance is the most dominant aspect of any galaxy," said lead author Pieter van Dokkum of Yale University. "For decades, we thought that galaxies start their lives as blobs of dark matter. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. NGC1052-DF2 challenges the standard ideas of how we think galaxies form."

The research, published in the March 29th issue of the journal Nature, amassed data from the Gemini North and W. M. Keck Observatories, both on Maunakea, Hawai'i, the Hubble Space Telescope, and other telescopes around the world.

Given its large size and faint appearance, astronomers classify NGC1052-DF2 as an ultra-diffuse galaxy, a relatively new type of galaxy that was first discovered in 2015. Ultra-diffuse galaxies are surprisingly common. However, no other galaxy of this type yet-discovered is so lacking in dark matter.

"NGC1052-DF2 is an oddity, even among this unusual class of galaxy," said Shany Danieli, a Yale University graduate student on the team.

To peer even deeper into this unique galaxy, the team used the Gemini Multi Object Spectrograph (GMOS) to capture detailed images of NGC1052-DF2, assess its structure, and confirm that the galaxy had no signs of interactions with other galaxies.

"Without the Gemini images dissecting the galaxy's morphology we would have lacked context for the rest of the data," said Danieli. "Also, Gemini's confirmation that NGC1052-DF2 is not currently interacting with another galaxy will help us answer questions about the conditions surrounding its birth."

Van Dokkum and his team first spotted NGC1052-DF2 with the Dragonfly Telephoto Array, a custom-built telescope in New Mexico that they designed to find these ghostly galaxies. NGC1052-DF2 stood out in stark contrast when comparisons were made between images from the Dragonfly Telephoto Array and the Sloan Digital Sky Survey (SDSS). The Dragonfly images show a faint "blob-like" object, while SDSS data reveal a collection of relatively bright point-like sources.

In addition to the Gemini observations, to further assess this inconsistency the team dissected the light from several of the bright sources within NGC1052-DF2 using Keck's Deep Imaging Multi-Object Spectrograph (DEIMOS) and Low-Resolution Imaging Spectrometer (LRIS), identifying 10 globular clusters. These clusters are large compact groups of stars that orbit the galactic core.

The spectral data obtained on the Keck telescopes revealed that the globular clusters were moving much slower than expected. The slower the objects in a system move, the less mass there is in that system. The team's calculations show that all of the mass in the galaxy could be attributed to the mass of the stars, which means there is almost no dark matter in NGC1052-DF2.

"If there is any dark matter at all, it's very little," van Dokkum explained. "The stars in the galaxy can account for all of the mass, and there doesn't seem to be any room for dark matter."

"Keck is in a very small group of telescopes that could even attempt these observations, because you need a large telescope to measure these accurate velocities," van Dokkum added. "Keck also has some of the best spectrographs in the world for measuring the velocities of faint objects. We had the opportunity to check and make sure we got the same result within the uncertainties, and that gave us confidence that we were doing things right."

The team's results demonstrate that dark matter is separable from galaxies. "This discovery shows that dark matter is real - it has its own separate existence apart from other components of galaxies," said van Dokkum.

NGC1052-DF2's globular clusters and atypical structure has perplexed astronomers aiming to determine the conditions this galaxy formed under.

"It's like you take a galaxy and you only have the stellar halo and globular clusters, and it somehow forgot to make everything else," van Dokkum said. "There is no theory that predicted these types of galaxies. The galaxy is a complete mystery, as everything about it is strange. How you actually go about forming one of these things is completely unknown."

However, researchers do have some ideas. NGC1052-DF2 resides about 65 million light years away in a collection of galaxies that is dominated by the giant elliptical galaxy NGC 1052. Galaxy formation is turbulent and violent, and van Dokkum suggests that the growth of the fledgling massive galaxy billions of years ago perhaps played a role in NGC1052-DF2's dark-matter deficiency.

Another idea is that a cataclysmic event within the oddball galaxy, such as the birth of myriad massive stars, swept out all the gas and dark matter, halting star formation.

These possibilities are speculative, however, and don't explain all of the characteristics of the observed galaxy, the researchers add.

The team continues the hunt for more dark-matter-deficient galaxies. They are analyzing Hubble images of 23 other diffuse galaxies. Three of them appear to share similarities with NGC1052-DF2, which van Dokkum plans to follow up on in the coming months at Keck Observatory.

"Every galaxy we knew about before has dark matter, and they all fall in familiar categories like spiral or elliptical galaxies," van Dokkum said. "But what would you get if there were no dark matter at all? Maybe this is what you would get."
-end-
Science Contacts:

Pieter van Dokkum
Astronomy Department
Yale University
Email: pieter.vandokkum"at"yale.edu
Phone: 203-432-5048

Shany Danieli
Astronomy Department
Yale University
Email: shany.danieli"at"yale.edu
Phone: 857-919-3674

Media Contacts:

Mari-Ela Chock
W.M. Keck Observatory
Email: mchock"at"keck.hawaii.edu
Phone: 808-554-0567

Jasmin Silva
Gemini Observatory
Email: jsilva"at"gemini.edu
Desk: 808 974-2575

Association of Universities for Research in Astronomy (AURA)

Related Dark Matter Articles:

Does dark matter annihilate quicker in the Milky Way?
Researchers at the Tata Institute of Fundamental Research in Mumbai have proposed a theory that predicts how dark matter may be annihilating much more rapidly in the Milky Way, than in smaller or larger galaxies and the early Universe.
Origin of Milky Way's hypothetical dark matter signal may not be so dark
A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars.
A new look at the nature of dark matter
A new study suggests that the gravitational waves detected by the LIGO experiment must have come from black holes generated during the collapse of stars, and not in the earliest phases of the Universe.
Dark matter may be smoother than expected
Analysis of a giant new galaxy survey, made with ESO's VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought.
Supercomputer comes up with a profile of dark matter
In the search for the mysterious dark matter, physicists have used elaborate computer calculations to come up with an outline of the particles of this unknown form of matter.
Mapping the 'dark matter' of human DNA
Researchers from ERIBA, Radboud UMC, XJTU, Saarland University, CWI and UMC Utrecht have made a big step towards a better understanding of the human genome.
Reconciling dwarf galaxies with dark matter
Dwarf galaxies are enigmas wrapped in riddles. Although they are the smallest galaxies, they represent some of the biggest mysteries about our universe.
Did gravitational wave detector find dark matter?
When an astronomical observatory detected two black holes colliding in deep space, scientists celebrated confirmation of Einstein's prediction of gravitational waves.
Dark matter does not contain certain axion-like particles
Researchers at Stockholm University are getting closer to corner light dark-matter particle models.
SDU researchers present a new model for what dark matter might be
There are indications that we might never see the universe's mysterious dark matter.

Related Dark Matter Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Setbacks
Failure can feel lonely and final. But can we learn from failure, even reframe it, to feel more like a temporary setback? This hour, TED speakers on changing a crushing defeat into a stepping stone. Guests include entrepreneur Leticia Gasca, psychology professor Alison Ledgerwood, astronomer Phil Plait, former professional athlete Charly Haversat, and UPS training manager Jon Bowers.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".