Gas cloud 20 times larger than the Milky Way may have been left behind by a cosmic invader, study reveals
Scientists have discovered a giant trail of gas drifting from a quintet of belligerent galaxies. The mysterious cloud of gas — the largest ever seen around a group of galaxies — may have been left behind by a “cosmic invader,” a new study reveals.
The cloud — an unexplained 2 million light-year-wide stream of hydrogen gas emanating from the galactic group known as Stephan’s Quintet — was discovered by the deepest scan ever of the region by the 500-meter Aperture Spherical Telescope (FAST) in China. Researchers think the gas trail,, may have formed “tidal debris” after swirling galaxies collided with a large cosmic invader about 1 billion years ago.
Named after the 19th-century discoverer, French astronomer Édouard Stephan, Stephan’s Quintet is a group of five galaxies “locked in a cosmic dance of repeated close encounters,” according to NASA, as they endlessly orbit and pirouette past each other. to spin. The quintet, located about 300 million light-years from Earth, is the first compact galaxy group ever observed and has been imaged by numerous telescopes, including the Hubble Space Telescope and the James Webb Space Telescope. Now, new research, conducted with FAST and published Oct. 19 in the journal Nature (opens in new tab)has looked 100 times deeper into the galaxy group than ever before, revealing the huge cloud of gas that emanates from it.
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“This is the largest atomic gas structure ever found around a galaxy group,” Xu Congsaid the study’s lead author and an astronomer from the National Astronomical Observatories of the Chinese Academy of Sciences, in a pronunciation.
The gas cloud was formed about 1.5 billion years ago, when an unknown interaction stripped atomic hydrogen from the galaxies and spewed it around. The researchers blame one or more fast-moving galaxies that collided with the quintet, and they’ve even identified a possible culprit: the galaxy NGC 7320a, which is currently hurtling through the cosmos at nearly 15 million miles per hour.
“A hypothetical scenario for the formation of the diffuse feature is that NGC 7320a … passed through Stephan’s Quintet about 1.5 billion years ago … see now,” the astronomers wrote in the study.
Alternatively, the gas cloud may have been sparked by a head-on collision between one of the quintet’s galaxies and another wandering galaxy, such as the galaxy Anon 4. A head-on collision would have created a shock wave that pushed the hydrogen out into a growing halo around the group, the researchers wrote. Another possibility is that the trail may not come from a galactic collision at all, but from the remnants of the original gas cloud that formed one or more of the quintet’s galaxies.
Regardless of what caused the trail, scientists also don’t know how the gas has been trapped for so long. Astronomers don’t usually expect gas clouds to survive more than 500 million years because exposure to ultraviolet radiation from stars tends to ionize them until they disappear. The researchers think the low-density cloud is leaking energy absorbed by the stars into its surroundings, but to understand how this would happen requires further research. The answer can provide insight into how galaxies are born and how they grow.
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