M82: A Starburst Galaxy

What Do These Images Tell Us?

X-ray

NASA/CXC/SAO /PSU/CMU The images show various views of M82. The Roentgen satellite (Rosat) X-ray image shows an expanding bubble of 6 million degree Celsius gas that extends 20,000 light years on either side of the galaxy. The hot gas bubble, or galactic wind, was created by the very high supernova rate of M82. The X-ray image also shows evidence for a strong source of X-rays in the center of the galaxy. Chandra observations should tell whether this source is due to matter falling into a supermassive black hole.

Optical

M. Weiland, Astronomy Interest Group, U.Constance A close encounter with the large galaxy M81 (lower galaxy in optical image at left) in the last 10 million years is thought to have triggered the burst of star formation in M82 (upper galaxy in optical image at left). For this reason, M82 is called a starburst galaxy. The stars do not form all at once, but over a period of a few millions years. The rate at which stars are forming in M82 is fifty to a hundred times that for a normal galaxy its size.

D. Strickland Since very massive stars use up their fuel and explode in a few million years, a star explodes about every ten years in M82. These violent explosions heat the surrounding gas to produce the expanding hot bubble. The hot gas blasts out of the galaxy along the path of least resistance, perpendicular to the plane of the galaxy, as shown in the combined optical and X-ray image.

NASA, LHEA An optical image taken with a filter to isolate light emitted by hydrogen atoms (H-alpha filter) at temperatures of about 10000 degrees Kelvin shows a bright network of filaments. The filaments are thought to be gas clouds that have been overtaken by the expanding hot wind and heated by shock waves or radiation from hot young stars.

P.Challis, Whipple Obs, Mt. Hopkins An optical image taken over a broad range of visible wavelengths shows an irregular, blotchy galaxy. The blotchiness is due to dust, which blocks much of the visible light from the galaxy.

Infrared

SAO Stars tend to form in dusty regions, so the bright spots in the infrared image show where stars are being formed. Newly formed stars radiate strongly and heat up the dust cloud that surrounds them producing bright infrared sources. M82 is the brightest infrared galaxy.

Radio

MERLIN & VLA The radio image shows a region about 3000 by 2000 light year across. It was made by combining data from the United Kingdom's MERLIN (Multi--Element Radio--linked Radio Interferometer) with data from the Very Large Array (VLA) in New Mexico. The small bright patches are the remnants of supernovas that have occurred in the last thousand years, and the large diffuse patches are thought to be caused by the accumulation of thousands of supernovas.