“Ongoing galaxy formation” detected
Courtesy Chandra X-ray Center
and World Science staff
Astronomers have reported finding a huge blob of hot gas around a spiral galaxy, evidence that galaxies like our Milky Way are drawing in material from a gradual inflow of intergalactic gas.
“What we are likely witnessing here is the ongoing galaxy formation process,” said Kristian Pedersen of the University of Copenhagen, Denmark, and lead author of a paper on the finding.
Images from NASA’s orbiting Chandra X-Ray Observatory show the glob,
the researchers said: it extends more than 60,000 light years on either side of the starry disk of a galaxy known as NGC
5746. A light year is the distance light travels in a year.
The discovery eases a long-standing problem for the theory of galaxy formation, the astronomers added.
Spiral galaxies are thought to form from enormous clouds of intergalactic gas that collapse to form great, spinning disks of stars and gas. The theory predicts large spiral galaxies should be immersed in blobs or “halos” of hot gas left over from the formation process.
Hot gas has been found around spiral galaxies before, but usually blowing outward rather than falling in, inconsistent with the theory, the researchers explained.
“Our observations solve the mystery of the missing hot halos around spiral galaxies,” said Pedersen. “The halos exist, but are so faint that an extremely sensitive telescope such as Chandra is needed to detect them.”
NGC 5746 is a massive spiral galaxy about a 100 million light years from Earth. Its starry disk is visible almost edge-on. The astronomers
believe the hot gas their instruments detected isn’t blowing outward, because there seem to be no ongoing processes that would cause this, such as bursts of star formation or violent activity in the core of the galaxy.
If the gas isn’t going outward, it is
probably moving inward, attracted by the galaxy’s gravity, they
“What we found is in good agreement with computer simulations in which galaxies are built up gradually from the merger of smaller clouds of hot gas and dark matter,” said Jesper Rasmussen of the University of Birmingham, United Kingdom and a coauthor of the report.
The simulations were carried out by Jesper Sommer-Larsen, also a co-author of the report, and collaborators at the University of Copenhagen. The paper is to
appear in the April issue of the research journal New Astronomy.
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