Found: A missing hot halo

X-ray observations of the massive spiral galaxy NGC 5746 reveal a spherical halo of hot gas (blue) extending 60,000 light-years on either side of the galaxy’s visible disk (seen edge on as a large white streak).

K. Pedersen, et al., NASA, CXC, Univ. Copenhagen, Palomar DSS

Because NGC 5746, which is 100 million light-years from Earth, doesn’t form stars prodigiously or have an energetic core, it’s not likely that the halo is gas streaming from the galaxy. Instead, it’s probably composed of inflowing material left over from the galaxy’s formation. NASA’s orbiting Chandra X-ray Observatory recorded the halo, and the galaxy’s disk was captured by a visible-light telescope on Earth.

Although galaxy-formation models have predicted halos of inflowing gas around massive spirals, this is the first such halo that astronomers have detected. NASA released the image on Feb. 3.

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