July 3
To mark the Fourth of July, the astronomers behind the Hubble Space Telescope present a fireworks show of cosmic proportions, featuring the starburst galaxy known as NGC 4449. The galaxy's blaze of stellar formation has been going on for billions of years, but it appears to be in the midst of an upswing - perhaps brought on by gravitational interaction with neighboring galaxies 12.5 million light-years away.
In the image released today, bluish-white clusters of hot, massive stars are scattered throughout the galaxy, interspersed with reddish regions of dusty star formation. The starlight throws dark clouds of dust and gas into silhouette.
Hubble's science team says the galaxy-wide starburst resembles what might be seen much farther away in primordial star-forming galaxies, which grew by sweeping up smaller stellar systems.
"Since NGC 4449 is close enough to be observed in great detail, it is the ideal laboratory for the investigation of what may have occurred during galactic formation and evolution in the early universe," the team says.
There are plenty of galaxies in NGC 4449's neighborhood, in the constellation Canes Venatici, leading astronomers to think that the gravitational interaction between those galaxies is creating the pressures leading to the starburst. They also think NGC 4449 can keep this up for only another billion years or so.
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