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Astronomers uncover hottest early galaxy cluster and starless dark matter cloud
Astronomers unveiled two groundbreaking discoveries this week at the American Astronomical Society meeting in Phoenix, challenging core theories on galaxy formation and dark matter. They identified the oldest and hottest galaxy cluster ever observed, along with the first confirmed detection of a starless dark matter cloud a "failed galaxy" preserved unchanged for billions of years. These findings offer rare glimpses into the universe's earliest epochs.
A team led by Dazhi Zhou, a doctoral student at the University of British Columbia, detected unusually scorching gas in the galaxy cluster SPT2349-56, located about 12 billion light-years from Earth. This cluster formed just 1.4 billion years after the Big Bang, yet its intracluster gas reaches temperatures akin to the Sun's core at least five times hotter than current theoretical models predict.
"We did not expect to observe such a hot cluster atmosphere so early in cosmic history," Zhou said in a statement. "In fact, I was initially skeptical of the signal because it was too strong to be real." Published January 5 in Nature, the results upend established models positing gradual gas heating over billions of years. The compact core, spanning roughly 500,000 light-years, hosts over 30 starburst galaxies producing stars at 5,000 times the Milky Way's rate. Newly found supermassive black holes within the cluster likely injected massive energy into surrounding gas, heating it far sooner than anticipated.
In a separate breakthrough, Hubble Space Telescope observations confirmed Cloud-9, the first verified example of a neutral hydrogen cloud bounded by reionization a gas cloud dominated by dark matter without stars. Positioned about 14 million light-years away near the spiral galaxy Messier 94, Cloud-9 holds around one million solar masses of hydrogen gas enveloped in a dark matter halo roughly five billion times the Sun's mass.
Gagandeep Anand, a scientist at the Space Telescope Science Institute who led the study, described Cloud-9 at the conference as a cosmic fossil that never gathered enough material to ignite star formation. "Nothing comparable to this has been discovered in the cosmos until now," said Rachael Beaton, an astronomer at the same institute, during Monday's presentation. "It's essentially a galaxy that never managed to form." Initially published in The Astrophysical Journal Letters in November 2025, the finding supports a key prediction of the Lambda-CDM cosmological model: dark matter halos that trap gas but fail to spawn stars.
