September 9, 2013

The Cigar Galaxy, a starburst galaxy in Ursa Major

Image Credit: NASA, ESA and the Hubble Heritage Team STScI/AURA)

Acknowledgment: J. Gallagher (University of Wisconsin), M. Mountain (STScI) and P. Puxley (NSF)

Messier 82 (also known as the Cigar Galaxy, NGC 3034 or Arp 337) is an edge-on spiral galaxy that lies approximately 11.5 million light-years away from Earth in the constellation of Ursa Major (the Great Bear), while it is receding from us at about 203 kilometers per second. It is a member of the M81 Group, a group of around 34 galaxies.

At its center lies a supermassive black hole with a mass of approximately 30 million solar masses, and approximately 600 light-years away from the center lies one of the first known intermediate-mass black holes, of roughly 200 to 5000 solar masses.

Being five times as bright in infrared light as the whole Milky Way and one hundred times as bright as our galaxy’s center, Messier 82 is the prototype nearby starburst galaxy. Throughout the galaxy’s center, young stars are being born 10 times faster than they are inside our entire Milky Way Galaxy. The fierce galactic superwind generated from these stars compresses enough gas to make millions of more stars.

Messier 82 is gravitationally bound to and interacting with Messier 81 (Bode’s Galaxy). The cores of the two galaxies are currently only 150,000 light-years apart, and the galaxies are orbiting each other about once every hundred million years, probably as a result of a near-collision about six hundred million years ago. Each time they pass each other, they undergo episodes of vigorous star formation caused by their gravitational interaction.

Tidal forces caused by gravity have deformed Messier 82 and are responsible for the starburst in its central portion, which is violently blowing huge amounts of gas and dust out of the galaxy, and emitting huge amounts of radiation, all the way from the infrared, to the X-ray region.

The rapid rate of star formation in this galaxy eventually will be self-limiting. When star formation becomes too vigorous, it will consume or destroy the material needed to make more stars. The starburst then will subside, probably in a few tens of millions of years.

This image highlights flame-like plumes of red glowing hydrogen gas blasting out from its central regions by a “superwind” created by large numbers of young, massive stars formed by the galaxy’s most recent interaction with Messier 81. The filaments of glowing gas, smoke and dust extend even further than previously suspected — nearly twenty thousand light-years above and below the plane of the galaxy.

In visible light Messier 82 shows two symmetric spiral arms, a complex network of dusty filaments and numerous tiny but massive globular clusters in the starburst core (Hubble counted 197). Usually, globular clusters, such as those in our own Milky Way galaxy, are ten to twelve billion years old, and date to the earliest days of galaxy formation. The globular clusters in Messier 82 however, are only 600 million years old (practically newborns, by stellar standards).

The starburst that is still going on right now occurred as a result of the most recent passage of Messier 81 by Messier 82, sometime within the last hundred million years; but a far more spectacular stage of star formation must have accompanied the formation of these young globular clusters, which may well have been caused by a near-collision of the two galaxies a little over half a billion years ago.

Each hundred-million year passage will probably bring the two galaxies closer together. At first, this will probably produce more and more extreme waves of star formation; but within a few billion years, the two galaxies should tear each other to pieces, and after a period of considerable chaos, merge into a new, larger galaxy.

Most of the pale, white objects sprinkled around the body of Messier 82 that look like fuzzy stars are actually individual star clusters about 20 light-years across and contain up to a million stars.

This image was made in March 2006, with the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. Astronomers assembled this six-image composite mosaic by combining exposures taken with four colored filters that capture starlight from visible and infrared wavelengths as well as the light from the glowing hydrogen filaments.