Two mysterious galaxies, devoid of darkish matter, may have a smashing origin story.
About 8 billion years in the past, researchers suggest, two dwarf galaxies slammed into each other. That cosmic crash brought about the gasoline inside these two galaxies to separate up and type a number of new dwarf galaxies, together with the 2 darkish matter–free ones.
A newfound row of dwarf galaxies, greater than 6 million light-years lengthy, may have shaped within the aftermath of the hypothesized crash, researchers report within the May 19 Nature. If appropriate, the discovering may assist remedy the thriller of how such uncommon darkish matter–free galaxies type, and reveal new particulars in regards to the nature of darkish matter.
Sign Up For the Latest from Science News
Headlines and summaries of the newest Science News articles, delivered to your inbox
Thank you for signing up!
There was an issue signing you up.
But different scientists are skeptical that there’s sufficient proof to assist this backstory. “If this is true, I think it would be really exciting. I just don’t think the bar has been met,” says astronomer Michelle Collins of the University of Surrey in Guildford, England.
In 2018, Yale University astronomer Pieter van Dokkum and colleagues reported a dwarf galaxy with no darkish matter (SN: 3/28/18). The invisible, mysterious substance is usually detectable in galaxies by way of its gravitational results on stars. When a second darkish matter–free dwarf galaxy was discovered within the neighborhood in 2019, it raised an apparent query: How did the 2 oddball galaxies type? Dark matter is mostly thought to type the inspiration of all galaxies, gravitationally attracting the gasoline that ultimately kinds stars. So some course of will need to have separated the darkish matter from the galaxies’ gasoline.
Scientists have beforehand seen darkish matter and regular matter separate on a really massive scale within the Bullet Cluster, which shaped when two clusters of galaxies rammed into each other (SN: 8/23/06). Other researchers had proposed that one thing related may occur with colliding dwarf galaxies, what van Dokkum and colleagues name “bullet dwarfs.”
In such a collision, the dwarf galaxies’ ethereal darkish matter would proceed on unperturbed, as a result of the darkish matter doesn’t work together with different matter. But the gasoline from the 2 galaxies would slam collectively, ultimately forming a number of clumps that might every change into its personal galaxy, freed from darkish matter.
Now, van Dokkum and colleagues say that the bullet dwarf concept explains the 2 beforehand reported darkish matter–free galaxies — and a number of other different galaxies close by. The two galaxies are shifting away from one another as if that they had come from the identical spot, the researchers say. What’s extra, the 2 galaxies are a part of a sequence of 11 galaxies aligned in a row, a construction that would have shaped within the aftermath of a bullet dwarf collision.
Two galaxies discovered to be freed from darkish matter, NGC 1052-DF2 and NGC 1052-DF4, are a part of a line of 11 galaxies whole (proven in insets). That linear association of galaxies may have been produced by an historical collision of two progenitor galaxies.P. van Dokkum et al/Nature 2022Two galaxies discovered to be freed from darkish matter, NGC 1052-DF2 and NGC 1052-DF4, are a part of a line of 11 galaxies whole (proven in insets). That linear association of galaxies may have been produced by an historical collision of two progenitor galaxies.P. van Dokkum et al/Nature 2022
“It’s super satisfying to finally have an explanation for these weird objects,” van Dokkum says.
But, Collins says, “there could be much more done to make it convincing.” For instance, she says, the scientists didn’t measure the distances of all of the galaxies from Earth. That means a number of the galaxies might be a lot farther away than others, and it might be a coincidence that the galaxies look like lined up from our viewpoint.
And the researchers haven’t but measured the velocities of all of the galaxies within the path or decided whether or not these galaxies are additionally lacking their darkish matter, which might assist affirm whether or not the situation is appropriate.
Other scientists are extra optimistic. “The origin story is very plausible in my opinion,” says astrophysicist Eun-jin Shin of Seoul National University in South Korea. Shin cowrote a perspective article on the invention with astrophysicist Ji-hoon Kim, additionally of Seoul National University, that was additionally revealed in Nature.
Computer simulations carried out by Shin, Kim and others have proven that bullet dwarfs can produce such darkish matter–free galaxies. If confirmed, the bullet dwarf concept may assist pin down darkish matter’s properties, specifically whether or not darkish matter interacts with itself (SN: 4/5/18).
Van Dokkum and colleagues are planning further measurements that would affirm or refute the case. But up to now, he says, “It has, to me, the ring of truth.”
