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What is a galaxy without stars called?
Earlier this month, radio astronomers announced that they had discovered the darkest galaxy ever seen, a cloud of hydrogen gas that resembles our own Milky Way galaxy in many ways, such as its mass and rotation, but without stars to support it. no one can discern.
“What we could have here… could “It is the discovery of a primordial galaxy, a galaxy that is so diffuse that it has not been able to form stars easily,” Karen O’Neil of Green Bank Observatory in West Virginia said in a news conference at a meeting of the American Astronomical Society in New Orleans on January 8.
That same week, a group of Spanish astronomers led by Mireia Montes, a researcher at the Institute of Astrophysics of the Canary Islands, revealed the discovery of another galaxy almost without stars, which they called Cloud.
“With our current knowledge, we do not understand how a galaxy with such extreme characteristics can exist,” Dr. Montes said. in a sentence disseminated by the institute. Dr. Montes is the first author of the new article, which was published in the journal Astronomy & Astrophysics.
And so, we can add “dark galaxies” to “dark matter,” “dark energy,” and other dark terms already in the cosmic lexicon.
Dark galaxies are entities whose stars are so few and faint that their light cannot be discerned other than as a fine, transparent haze that does not appear to contain any stars. (At first, dark galaxies were referred to as “low surface brightness galaxies” or “ultradiffuse galaxies,” but time and jargon move on.) As astronomers continue to probe deeper into the heavens with more powerful and intelligent eyes, dark galaxies have begun to appear more frequently, challenging long-held views about the formation and evolution of galaxies.
The accidental galaxy
These faint ghosts are hard to find and even harder to study, requiring hours or days of observing to focus their visible starlight. One way is to scan the skies with radio telescopes tuned to the frequency of interstellar hydrogen gas that permeates galaxies.
Dr O’Neil was part of such a study, involving a variety of telescopes, of about 350 low surface brightness galaxies. “I mistyped the coordinates of the galaxy I intended to observe, which caused the telescope to point to a different part of the sky than intended,” he recently said in an email. The telescope landed on something she had never seen before.
“It is a galaxy made only of gas; it has no visible stars,” he said. “Stars could be there, we just can’t see them.”
The galaxy, known as J0613+52, is about 270 million light years away. It is swimming among two billion solar masses of primordial hydrogen that was produced in the Big Bang, but the galaxy is not forming any stars, probably because the gas is too diffuse to clump together in clouds that become stars. Furthermore, there are no nearby galaxies with a gravitational influence that could cause such a cluster.
“J0613+52 appears to be intact and underdeveloped,” Dr. O’Neil said. “This could be our first discovery of a nearby galaxy made up of primordial gas.”