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


A research co-led by physicists at UC Riverside and UC Irvine has discovered that darkish 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 — fuel and stars — is way more unfold out in ultra-diffuse galaxies in comparison with “regular” galaxies with related lots. 

Hai-Bo Yu is a theoretical physicist at UC Riverside. (Samantha Tieu)

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, a long-term collaborator of Yu’s, have printed in The Astrophysical Journal about newly found ultra-diffuse galaxies and their darkish matter halos.

Yu and Kaplinghat have 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 a part of UCR this fall.

The analysis was supported by grants from the Nationwide Science Basis, Division of Vitality, John Templeton Basis, Nationwide Aeronautics and Area Administration, Netherlands Analysis College for Astronomy, and ASTRON, the Netherlands Institute for Radio Astronomy.

Q. What’s a darkish matter halo?

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

Q. You’ve discovered darkish 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 huge in comparison with, say, the Milky Method. They comprise lots of fuel, nevertheless, they usually have a lot greater fuel mass than complete stellar mass, which is reverse to what we see within the Milky Method. The ultra-diffuse galaxies even have giant sizes.

The distribution of darkish matter in these galaxies will be inferred from the movement of fuel particles. What actually surprises us is that the presence of baryonic matter itself, predominantly within the type of fuel, is almost adequate to elucidate the measured velocity of fuel particles and leaves little room for darkish matter within the internal areas, the place a lot of the stars and fuel are situated. 

That is very stunning as a result of within the case of regular galaxies, whose lots are much like these of the ultra-diffuse galaxies, it’s the other: darkish matter dominates over baryonic matter. To accommodate this outcome, we conclude that these darkish matter halos will need to 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, darkish matter halos of the ultra-diffuse galaxies are “odd.”

At first look, one would anticipate that such low-concentration halos are so uncommon that the ultra-diffuse galaxies wouldn’t even exist. After trying into the info from state-of-the-art numerical simulations of cosmic construction formation, nevertheless, we discovered the inhabitants of low-concentration halos is greater 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 specialists on fuel dynamics of galaxies. They found that the ultra-diffuse galaxies rotate extra slowly than regular galaxies with related lots. We labored collectively to interpret measurement knowledge of the fuel movement of those galaxies and infer their darkish matter distribution. Moreover, we analyzed knowledge from simulations of cosmic construction formation and recognized darkish matter halos which have related properties as these inferred from the ultra-diffuse galaxies.

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

Now we have many questions concerning the formation and evolution of those newly found galaxies. For instance, the ultra-diffuse galaxies comprise lots of fuel and we have no idea how this fuel 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 just isn’t nicely understood, and extra work is required. 

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

These are superb objects to check due to their stunning 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, most likely even the character of darkish matter. 





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