Earlier this year astronomers detected a galaxy whose existence was seemingly impossible. Now, astronomers have debunked about galaxies without dark matter.
The galaxy in question is much closer than proposed original measurements, according to fresh distance calculations. This changes the galaxy’s mass as a whole, as well as the proportion of that mass that could be normal.
It actually looks like a fairly normal galaxy on the basis of this new measurement. It’s called NGC 1052-DF4 (or in short DF4), and it seemed to support a past finding when Yale astronomers discovered it. The galaxy NGC 1052-DF2 (or DF2), whose mass and dynamics indicated it had no dark matter whatsoever.
But just last month, another team of astronomers dropped a bombshell. They had recalculated the distance to DF2 and discovered it wasn’t, as earlier found, 64 million light-years away (around 20 megaparsecs), but only 42 million light-years (13 Mpc) away from Earth.
Now astrophysicists Ignacio Trujillo and Matteo Monelli from the Instituto de Astrofísica de Canarias have applied their methods to DF4, returning a comparable outcome that is presently available on arXiv’s preprint website.
DF4 seems to be not 20 Mpc away from where we’re all sitting, but just 14.2 Mpc away.
Trujillo informed us his interest was piqued by the initial discovery of DF2. He was not only fascinated by the alleged absence of dark matter, but by the globular clusters. These are big clusters of stars orbiting galactic centres and are seen in galaxies of all types.
According to Trujillo, “All the galaxies we know about, so our galaxy, the Andromeda galaxy, the dwarf galaxies, and so on, have a population of more or less the same globular clusters. But the globular clusters of DF2 are extremely large and bright. So bright that they have no counterpart in the rest of the galaxies we know.”
So, he worked out a quick calculation: how far would the globular clusters of DF2 need to be to have normal luminosity? And what is the standard size range? This range was 13 Mpc in two separate, independent calculations.
The next stage was the distance measurement. This figure also turned out to be 13 Mpc using five different measurement techniques.
Another even more extreme was reported and it caught my attention that it was exactly on the same field of view. Maybe they are doing the same mistake.” Trujillo said.
So, again the team of Trujillo went through the process. And they got a closer distance again. Trujillo thinks that the issue is that both galaxies are small, but the calibration of range measurement used by the Yale team was based on very huge galaxies and was poorly suited for DF2 and DF4.
Furthermore, Trujillo’s team discovered that there are two groups of galaxies in that specific field of view. One of them is around 20 Mpc away. This is the group that was initially believed to belong to DF2 and DF4. But the other is nearer. It’s at Mpc 13.5. So, it’s possible that the two galaxies were associated with the wrong group.
What this closer range would mean is that there would be less mass in the two galaxies, and the percentage of normal matter within-things we can see, like stars and gas-is smaller.
Objects like globular clusters orbit quicker with most galaxies than they should be based on the mass that we can detect directly. Some undetectable mass produces more gravity than normal matter can account for. We call this undetectable mass dark matter.
Farther away, the galaxies luminosity meant that there was sufficient ordinary mass of matter to generate those orbits. Trujillo noted it was even stranger with DF4: it went too far the other way around.
“The galaxy is so exotic that they cannot explain the dynamics even with the stars alone,” he said. “It’s so artificially low, the dynamics are so small, the velocities, that it has to be even larger with the stars they claim to have. So somehow to explain what they’ve got, they’d need some sort of anti-gravity, something very, very strange.”
But the fact that we’re just nearer to the galaxy ends up resolving the strangeness. Cosmologists believe that galaxies begin their life as a blob of dark matter, so long-lived galaxies that have none of the things would require a new galaxy formation model. These new measurements also solve this issue.
So, of the two alternatives-one being a pair of highly strange galaxies that break physics and cosmology, and the other being human error-the probability is likely not weirdness. Although it has not yet been fully resolved.
In a few months, there will be much greater information accessible from the Hubble Space Telescope, enabling both teams to review their results. And while Trujillo thinks that the Yale team’s distance measurements are inaccurate because the calibration was wrong, he also thinks that there is the chance of some weirdness.
“I’d love the galaxies are strange in the end,” said Trujillo. “Because that would mean something new and more to learn.”
The paper was accepted in The Astrophysical Journal Letters and is accessible on arXiv.