Image: Hubble sees elegant spiral hiding a hungry monster

October 19, 2015, NASA
Credit: ESA/Hubble & NASA

NGC 4639 is a beautiful example of a type of galaxy known as a barred spiral. It lies over 70 million light-years away in the constellation of Virgo and is one of about 1,500 galaxies that make up the Virgo Cluster.

In this image, taken by the NASA/ESA Hubble Space Telescope, one can clearly see the bar running through the bright, round core of the galaxy. Bars are found in around two-thirds of spiral galaxies, and are thought to be a natural phase in their evolution.

The galaxy's spiral arms are sprinkled with bright regions of active star formation. Each of these tiny jewels is actually several hundred light-years across and contains hundreds or thousands of newly formed stars. But NGC 4639 also conceals a dark secret in its core—a that is consuming the surrounding gas.

This is known as an (AGN), and is revealed by characteristic features in the spectrum of light from the galaxy and by X-rays produced close to the black hole as the hot gas plunges towards it.

Most galaxies are thought to contain a black hole at the center. NGC 4639 is in fact a very weak example of an AGN, demonstrating that AGNs exist over a large range of activity, from galaxies like NGC 4639 to distant quasars, where the is almost completely dominated by the emissions from the AGN.

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Tuxford
2 / 5 (4) Oct 19, 2015
As the galaxy core star grows evermore massive from producing new matter and ejecting therefrom at an ever-increasing rate likely preferentially along bipolar jets that precess in orientation more and more slowly as the core star grows bigger, then a bar of new stars would naturally form therefrom along the directions of these jets.

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