Why are dark matter halos of ultra-diffuse galaxies so odd?

A research co-led by physicists at UC Riverside and UC Irvine has discovered that dark matter halos of ultra-diffuse galaxies are very odd, elevating questions on physicists’ understanding of galaxy formation and the construction of the universe.

Extremely-diffuse galaxies are so referred to as due to their extraordinarily low luminosity. The distribution of baryons—gasoline and stars—is way more unfold out in ultra-diffuse galaxies in comparison with “regular” galaxies with related plenty.

Within the following Q&A, Hai-Bo Yu, an affiliate professor of physics and astronomy at UCR, shares his ideas on the findings he and UCI’s Manoj Kaplinghat, his long-term collaborator, have printed in The Astrophysical Journal about newly found ultra-diffuse galaxies and their dark matter halos.

Yu and Kaplinghat had been joined within the analysis by Demao Kong of Tufts College, and Filippo Fraternali and Pavel E. Mancera Piña of the College of Groningen within the Netherlands. First creator Kong will be part of UCR this fall.

Q. What’s a dark matter halo?

A dark matter halo is the halo of invisible matter that permeates and surrounds a galaxy or a cluster of galaxies. Though dark matter has by no means been detected in laboratories, physicists are assured dark matter, which makes up 85% of the universe’s matter, exists.

Q. You have discovered that dark matter halos of the ultra-diffuse galaxies are very odd. What’s odd about them and what are you evaluating them to?

The ultra-diffuse galaxies we studied are a lot much less large in comparison with, say, the Milky Way. They comprise lots of gasoline, nevertheless, they usually have a lot increased gasoline mass than total stellar mass, which is reverse to what we see within the Milky Way. The ultra-diffuse galaxies even have massive sizes.

The distribution of dark matter in these galaxies will be inferred from the movement of gasoline particles. What actually surprises us is that the presence of baryonic matter itself, predominantly within the type of gasoline, is sort of ample to elucidate the measured velocity of gasoline particles and leaves little room for dark matter within the internal areas, the place many of the stars and gasoline are positioned.

That is very shocking as a result of within the case of regular galaxies, whose plenty are just like these of the ultra-diffuse galaxies, it is the other: Darkish matter dominates over baryonic matter. To accommodate this outcome, we conclude that these dark matter halos should have a lot decrease “concentrations.” That’s, they comprise a lot much less mass of their internal areas, in comparison with these of regular galaxies. On this sense, dark matter halos of the ultra-diffuse galaxies are “odd.”

At first look, one would count on that such low-concentration halos are so uncommon that the ultra-diffuse galaxies wouldn’t even exist. After trying into the information from state-of-the-art numerical simulations of cosmic construction formation, nevertheless, we discovered the inhabitants of low-concentration halos is increased than the expectation.

Q. What was concerned in doing the research?

This can be a collaborative work. Filippo Fraternali and his scholar Pavel E. Mancera Piña are consultants on gasoline dynamics of galaxies. They found that the ultra-diffuse galaxies rotate extra slowly than regular galaxies with related plenty. We labored collectively to interpret measurement information of the gasoline movement of those galaxies and infer their dark matter distribution. Moreover, we analyzed information from simulations of cosmic construction formation and recognized dark matter halos which have related properties as these inferred from the ultra-diffuse galaxies.

Q. Your findings increase questions on our understanding of galaxy formation/construction formation of the universe. How?

We’ve got many questions relating to the formation and evolution of those newly found galaxies. For instance, the ultra-diffuse galaxies comprise lots of gasoline and we have no idea how this gasoline is retained throughout galaxy formation. Additional, our outcomes point out that these galaxies could also be youthful than regular galaxies. The formation of the ultra-diffuse galaxies isn’t properly understood, and extra work is required.

Q. What makes ultra-diffuse galaxies so attention-grabbing?

These are wonderful objects to review due to their shocking properties, as mentioned in our work. The newly found ultra-diffuse galaxies present a brand new window for additional testing our understanding of galaxy formation, in all probability even the character of dark matter.