nov 172013

November 17, 2013

Messier 84, an elliptical or lenticular galaxy in Virgo

NGC 4374

Image Credit: Gary Bower, Richard Green (NOAO), the STIS Instrument Definition Team, and NASA/ESA

Messier 84 (also known as NGC 4374) is either an elliptical galaxy, or a giant lenticular galaxy seen face-on, located some 60 million light-years away from Earth in the constellation of Virgo (the Virgin), while it is receding from us at about 1060 kilometers per second.

It is situated in the heavily populated inner core of the Virgo Cluster of Galaxies, a grouping of around 1500 gravitational bound galaxies, and is one of its brighter members. Messier 84 is also part of Markarian’s Chain, a group of Virgo Cluster galaxies that lie along a smooth curve and have similar radial velocities.

Messier 84 is mainly populated by old yellowish stars. However, Messier 84 also has a few young stars and star clusters, indicating star formation at a very low rate. It’s nucleus shows conspicuous dark dust lanes.

In 1997, a disk of rapidly rotating gas and stars was discovered in Messier 84, about 26 light-years from its center. Only the gravitational pull of a supermassive black hole could account for this motion. Two jets of matter which are shooting out from the galaxy’s center are also indicating the presence of a monstrous supermassive black hole. Astronomers estimated that the mass of this black hole is about 1.5 billion times the mass of our Sun, what makes it one of the largest and most massive black holes yet discovered.

The jets of energetic particles heat surrounding clouds of gas to millions of degrees, preventing gas clouds from collapsing to form new stars. The jets span tens of thousands of light-years, and squirt into space at close to the speed of light.

Two supernovae have been observed in Messier 84: on May 18, 1957 the first one: SN 1957B, and on Dec 3, 1991 the second one: SN 1991bg, both Type Ia supernovae. Possibly, a third supernova occurred in this galaxy: a Type I supernova called SN 1980I on June 13, 1980. However, SN 1980I cannot be clearly associated with a single galaxy. Its apparent position is several arcminutes from the centers of three bright galaxies: Messier 84, NGC 4387, and Messier 86 (NGC 4406).

A Type Ia supernova is a result from the violent explosion of a white dwarf star (a compact star that has ceased fusion in its core).

This image, taken with Hubble’s Wide Field Planetary and Camera 2, shows the core of Messier 84 where the black hole dwells. Astronomers mapped the motions of gas in the grip of the black hole’s powerful gravitational pull by aligning the STIS’s spectroscopic slit across the nucleus in a single exposure.

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