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Tour: 'H' is for Hot and Huge in Chandra Image

With a single letter seemingly etched in the X-ray glow around it, a giant black hole at the center of a massive elliptical galaxy is making a mark on its surroundings.

This “H”-shaped structure is found in a detailed new X-ray map of the multimillion-degree gas around the galaxy Messier 84, or M84 for short.

As gas is captured by the gravitational force of the black hole, some of it will fall into the abyss, never to be seen again. Some of the gas, however, avoids this fate and instead gets blasted away from the black hole in the form of jets of particles. These jets can push out holes, or cavities, in the hot gas surrounding the black hole. Given the orientation of the jets to Earth and the profile of the hot gas, the cavities form what appears to resemble the letter “H”.

Astronomers used NASA’s Chandra X-ray Observatory to make a map of the hot gas in and around M84. In fact, Chandra was able see down to only about 100 light-years away from the black hole in the center of the galaxy. This gas radiates at temperatures in the tens of millions of degrees. The huge letter “H” is about 40,000 light-years tall, or about half the width of the Milky Way. The radio image from the NSF’s Very Large Array, or VLA, in New Mexico reveals jets streaking away from the black hole.

Researchers studying M84 with Chandra and the VLA found that the jets may influence the flow of the hot gas towards the black hole even more than the gravitational pull from the black hole. For example, matter is falling towards the black hole from the north — that is, along the direction of the jet — at a rate that is only a quarter of that from directions where the jet isn’t pointing, to the east and west. One possibility is that gas is lifted along the direction of the jet by the cavities, slowing the rate at which gas falls onto the black hole.

The authors also used the Chandra data from M84 to test something called Bondi accretion. Named for the scientist Herman Bondi, a scientist who was born in Australia and died in 2005, Bondi accretion is a model that considers how the material close to a black hole is affected by its gravity and falls inwards. The researchers saw that material in M84 is falling towards the black hole at different rates in different directions, disagreeing with the model for Bondi accretion.

M84 is a cousin to M87, the galaxy with the first black hole imaged with the Event Horizon. Located about 55 million light-years away, M84, like M87, is a member of the Virgo Cluster of galaxies.

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