By Popular Mechanics
Last year, astronomers thought they had discovered a bizarre new galaxy that threatened to challenge the fundamental principles of physics. It does not turn out that much.
Now, the galaxy, which scientists believe did not contain dark matter, looks much more normal. Scientists believe that the whole thing is a misjudgment.
The first questions surfaced in 201
"We thought that every galaxy has dark matter and that dark matter starts a galaxy," said Pieter van Dokkum of Yale University, New York, Connecticut, chief researcher of Hubble observations, NASA press release.
"This invisible, mysterious substance is the most dominant aspect of a galaxy," van Dokkum said. "So it's unexpected to find a galaxy without finding it, it challenges common beliefs about how galaxies work and shows that dark matter is real: it has its own existence, apart from other components of galaxies This result also suggests more than one way to make a galaxy. "
There was a lot about DF2 that puzzled scientists. Studies in recent years have estimated that dark matter accounts for 27 percent of the universe, which would account for 85 percent of all matter.
So, what exactly is dark matter? Well, it's a bit complicated.
"We are much safer, which is dark matter than we are, what it is," says NASA. Dark matter and the accompanying dark energy explain the accelerated expansion of the universe. There are theories like WIMPS (Weakly Interacting Massive Particles) or MACHOs (Massive Compact Halo Objects), but they remain just that.
But scientists are at least confident in saying that dark matter a.) Dark and b. ) the stuff that makes up most of the universe. Having a galaxy without dark matter would challenge a basic understanding of the universe.
Scientists had missed DF2 because it seemed to contain only 1/200 of the Milky Way's stars. When the results showed that the galaxy contained only 1/400 of the dark matter predicted by scientists, DF2 became a mystery 64 million light-years away.
In 2019, a second galaxy with similar characteristics appeared. Known as NGC 1052-DF4 (DF4), it seemed to confirm the results of DF2: "The discovery of a second galaxy with very little to no dark matter is as exciting as the first discovery of DF2," van Dokkum said in a press release ,
Now both claims are being examined by other scientists.
The first, DF2, was studied by astrophysicists Ignacio Trujillo, Matteo Monelli and others by the Instituto de Astrofísica de Canarias (IAC) based in Spain. Based on data from the Hubble Space Telescope, the Gemini Observatory and three other sources, Trujillo's team believes that the initial estimates for DF2 "overestimated the galaxy's distance". Instead of being 64 million light years away, a distance known as 20 megaparse seconds, it was only 42 million light-years or 13 megaparse seconds away from Earth.
"For a long time, this was (and still is) one of the most difficult tasks in astronomy," wrote Trujilo in an accompanying blog post. "How to measure the distance to objects we can not touch."
The distance of DF2 determines how scientists see the galaxy, which in turn determines how they estimate their mass. If it is only 13 megaparse seconds away, then DF2 would only be "about half the mass previously estimated," according to a press statement by the IAC, while "the mass of its stars is only about one quarter of the previously estimated mass."  If DF2 has a much lower mass than previously thought, Trujilo says, then it implies that a significant portion of the total mass must be dark matter.
And now Trujilo has DF4 in view. After his team applied his DF2 tactic on DF4, it released an article on the pre-print server arXiv, showing that the second galaxy is only 14.2 megaparsec away, as opposed to the 20 megaparsec that Yale has Team had originally accepted.
Speaking to ScienceAlert, Trujilo said that the rangefinding calibration methods used in Yale are "based on very massive galaxies" and accurate in galaxies such as DF2 and DF4. Popular Mechanics asked van Dokkum for a comment.
Further data on DF4 from the Hubble Space Telescope will be available in the coming months, allowing both sides to further analyze the distant dispute.
The study of galaxies is a complex and difficult topic. Earlier this year, the Hubble found a new galaxy quite by accident.
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