How big is NGC 3310?

NGC 3310 is a spiral galaxy in the constellation Ursa Major, roughly 40 million to 60 million light-years from Earth. Its bright disk is about 40,000 to 50,000 light-years across. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. NGC 3310 is a starburst galaxy, one that is forming new stars far faster than most galaxies.

Size

A galaxy has no sharp edge, so its width depends on how faint a glow is counted. A standard catalog of bright galaxies measures the disk of NGC 3310 at 3.1 arcminutes across on the sky. An arcminute is one-sixtieth of a degree.

Turning that angle into a width needs the distance, and the distance of NGC 3310 is not known precisely. Published distances range from about 43 million to 59 million light-years. At those distances, 3.1 arcminutes is about 39,000 to 53,000 light-years. NASA gives a round figure of about 50,000 light-years.

Beyond the disk lie faint streams of stars, debris from a collision. The farthest of them lie about 50,000 light-years from the center.

Size comparisons

NGC 3310 is roughly half the width of the Milky Way's disk, which is about 100,000 light-years across.
The Sombrero Galaxy, about 50,000 light-years across, is about as wide as NGC 3310 or a little wider.
Most of the galaxy's new stars form in a ring about 3,000 light-years across around its center. About 13 of these rings side by side would span the disk.
On the sky, NGC 3310 is about one-tenth the width of the full Moon.
If NGC 3310 were shrunk to the size of a basketball, Earth would be about 270 meters (870 feet) away.

A burst of new stars

Most galaxies form new stars slowly, but a starburst galaxy forms them at a very high rate. NGC 3310 turns gas into new stars at a rate of about 8.5 times the mass of the Sun each year. The Milky Way, which is about twice as wide, forms roughly two times the mass of the Sun each year.

Images from the Hubble Space Telescope show several hundred star clusters along the spiral arms. Each one formed up to about a million stars in less than 100,000 years. The clusters range in age from about one million to more than 100 million years. That suggests the burst of star formation began more than 100 million years ago and has kept going since.

Signs of a collision

NGC 3310 carries marks of a recent collision. A faint arc of stars on its west side, called the bow, curves about 20,000 light-years from the center. A chain of bright knots of young stars, called the arrow, stretches from about 13,000 to 29,000 light-years out. Two long tails of hydrogen gas extend from the galaxy, one to the northwest and one to the south.

A 2001 study of the hydrogen gas concluded that these features point to a recent merger of two gas-rich galaxies. A 2006 study of the faint streams of stars found signs that several small galaxies have been swallowed. NASA describes the likely cause of the starburst as a collision with a smaller galaxy about 100 million years ago.