How big is Tadpole Galaxy? | Scale of the Universe

The Tadpole Galaxy, also cataloged as UGC 10214 and Arp 188, is a disturbed spiral galaxy with a long tail of stars. From the far edge of its disk to the end of its tail, it is about 400,000 light-years long. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The galaxy is about 420 million light-years away, in the constellation Draco.

Size

The Tadpole's size is its length, measured along the disk and the tail together. Thomas Jarrett and colleagues found the main disk to be about 124,000 light-years across, with the tail reaching another 245,000 light-years beyond it. That makes about 370,000 light-years in all. The European Space Agency's Hubble team describes the tail as stretching more than 280,000 light-years, which would make the whole galaxy a little over 400,000 light-years long.

Hydrogen gas, detected with radio telescopes, extends along the tail too, for about 100,000 parsecs, or about 330,000 light-years. A parsec is about 3.26 light-years. The sizes also depend on the distance each study assumes, which is uncertain by several percent.

Size comparisons

The Tadpole's disk alone is a little wider than the disk of the Milky Way, which is about 100,000 light-years across. With its tail, the Tadpole is about four times as long as the Milky Way is wide.
If the Milky Way were shrunk to the size of a basketball, the Tadpole's disk would be about 30 centimeters (12 inches) across, and its tail would trail about 60 centimeters (2 feet) behind it.
The tail alone is about as long as the giant elliptical galaxy NGC 4889 is wide, about 250,000 light-years.
The whole Tadpole, tail included, is about one-sixth of the distance from the Milky Way to the Andromeda Galaxy, about 2.5 million light-years.

How the tail formed

The Tadpole's shape comes from a collision. A small, compact, very blue galaxy passed close to the Tadpole, and the small galaxy's gravity pulled on the Tadpole. The pull drew stars and gas out of the Tadpole's disk and stretched them into the long tail. Astronomers call a stream like this a tidal tail.

In Hubble's image, the intruder can still be seen through the upper left of the Tadpole's disk. That team describes it as a likely "hit and run" galaxy that is now leaving the scene. It holds less than a tenth as much gas as the Tadpole. Dividing the tail's length by the speed at which its gas was thrown out suggests that the encounter happened about 250 million years ago.

Young star clusters in the tail

Hubble's images show dozens of bright blue star clusters in the Tadpole's spiral arms and tail. Each one formed up to about a million stars. The clusters look blue because they contain very massive stars, which are about 10 times as hot as the Sun and a million times as bright.

Some clusters in the tail are only 3 to 10 million years old, much younger than the tail itself. They must have formed inside the tail long after the collision, not in the disk. Two large clumps of young stars in the tail are likely to become dwarf galaxies, small galaxies that will orbit the Tadpole.