All galaxies consist mainly of dark matter. Visible matter, such as stars, gas, and dust, constitutes only a small percentage of the mass of a galaxy. But galaxies like this one, called FAST J0139+4328, are even more extreme, and its dim light suggests there are no stars, just clouds of gas. Astronomers who discovered it claim that the galaxy presents itself "without any optical counterpart".
Images of FAST J0139+4328 showing the lack of optical counterpart. Credit: Xu et al. 2023
Astronomers have discovered the new dark galaxy thanks to the FAST and Pan-STAARS telescopes, it is a typical disk galaxy but has an extremely low magnitude and a reduced stellar mass. The results provided observational evidence that FAST J0139+4328 is an isolated dwarf galaxy that was first detected in the nearby universe.
Its redshift value puts it between about 1 million and 1.25 million light years away. It consists predominantly of a cloud of neutral hydrogen (Hi) rather than ionized hydrogen or molecular hydrogen.
The current Standard Cosmological Model explains the relationship between dark matter and galaxies. Dark matter halos contain galaxies as if dark matter provided the structure for their formation. The halo envelops the entire galactic disk and extends beyond the edge of the visible galaxy. Astronomers cannot see dark matter, but deduce its existence because of its effects on the objects around it. And halos play a fundamental role in the formation and evolution of galaxies according to our current models.
Astronomers think their gas failed to form the stars. This is why astronomers consider them fundamental to understanding how galaxies form and evolve. Gas-rich dark galaxies may reflect the first stage of galaxy formation.
This dark dwarf galaxy and others like it could also help solve a known problem in cosmology. The Cold Dark Matter (CDM) model predicts that there should be more dwarf galaxies than astronomers have been able to observe to date. This discrepancy is known as "the missing satellite problem" or even "the dwarf galaxy problem".
According to observations, the Milky Way has 11 dwarf galaxies and the entire Local Group has about 38. But the simulations of dark matter show that dwarf galaxies, as satellites of the Milky Way alone, should be over 500. Dark dwarf galaxies like this could fill this gap and strengthen our understanding of dark matter and the cosmos itself.
And while dark dwarf galaxies like this one are definitely weird, they’re not the only ones.
Astronomers have also discovered galaxies that contain little or no dark matter, although this discovery is still controversial.
The Dragonfly Galaxy 44 consists mainly of dark matter. Credit: Teymoor Saifollahi and NASA / HST
In 2018, a research team published a paper in Nature about the galaxy NGC 1052 DF2, which was found to be free of dark matter. NGC1052-DF2 demonstrated that dark matter is not always coupled with baryonic matter on galactic scales, and a subsequent article published in 2019 announced the detection of another dark matter-free galaxy in the same region called NGC 1052 DF4.
Now the authors of this discovery explain the importance of finding a dark dwarf galaxy. These dark dwarf galaxies may simply not have enough dark matter to hold their gas. It could be that the amount of gas is too small to trigger Toomre’s instability in the rotating disk of the galaxy. Without stars, these dark dwarf galaxies are extremely weak and difficult to detect and can only be seen by seeking neutral hydrogen rather than electromagnetic radiation.
It is expected that future high sensitivity and resolution HI surveys will greatly contribute to our understanding of the absence of ultra-weak galaxies and possibly track down what is now missing.
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1 commenti:
On the dark matter photo, there is what looks like a man at the very bottom of the matter photo .it's on the the bottom dead center on the dark matter object! Amazing!
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