starburst galaxy
Most galaxies build their stars at a steady, leisurely pace, like a bakery turning out a few loaves an hour. A starburst galaxy is a bakery in a frenzy — forming new stars so fast that it would burn through its entire gas supply in a cosmic blink. It is a galaxy caught in an intense, short-lived episode of furious star formation.
Concretely, our Milky Way makes new stars at a sedate rate of roughly one Sun's worth per year. A starburst galaxy can churn out tens, hundreds, even a thousand solar masses of new stars per year. That pace is unsustainable: at such a rate the galaxy would exhaust its gas in just tens of millions of years — a flash compared to a galaxy's lifetime — so the burst must be a temporary phase, not a steady state. The bursts are usually triggered when something dumps a lot of gas into a small region fast, most often a galaxy merger or close interaction, or a bar funneling gas to the center. The newborn massive stars are hot and blue, blaze in ultraviolet light, and heat surrounding dust until the galaxy glows brilliantly in the infrared.
Starbursts matter because they are when galaxies do a big share of their growing, and they show how violently star formation can switch on. The most extreme, dust-shrouded starbursts in the distant universe are among the most luminous galaxies known, often hidden at visible wavelengths but blazing in the infrared and submillimeter. Starbursts also drive powerful galactic winds that can blow gas out of the galaxy — a form of feedback that helps regulate, and eventually shut off, star formation.
M82, the Cigar Galaxy, is a nearby starburst: jolted by a close pass of its larger neighbor M81, its core is forming stars roughly ten times faster than the whole Milky Way, and superwinds of hot gas are visibly streaming out above and below its disk.
Star formation cranked to a frenzy — bright, blue, dusty, and necessarily brief.
A starburst is a temporary episode, not a permanent class: by definition the galaxy is burning gas far faster than it can be replaced, so the burst lasts only tens of millions of years before the fuel runs low and the galaxy calms down.