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April 1, 2013

NGC 1409 & NGC 1410, two interacting galaxies in Taurus

NGC 1409 and 1410, two interacting galaxies in Taurus

Image Credit: NASA and W.C. Keel (University of Alabama)

NGC 1409 (right) and NGC 1410 (left), together also known as UGC 2821, are two interacting galaxies located about 300 million light-years away in the constellation of Taurus, the Bull. Their centers are only 23,000 light-years apart. The galaxies are bound together by gravity, orbiting each other at 1 million kilometers (670,000 miles) an hour, while they are speeding away from Earth at about 7750 and 7590 kilometers per second respectively.

There is an intergalactic “pipeline” of material flowing between two battered galaxies that bumped into each other about 100 million years ago. The pipeline – the dark string of matter – begins in the elliptical galaxy NGC 1410, crosses over the intergalactic space between them, and wraps around the lenticular galaxy NGC 1409.

It is believed that the tussle between these compact galaxies somehow created the pipeline, but it’s not certain why NGC 1409 was the one to begin gravitationally siphoning material from its partner. And it isn’t known where the pipeline begins in NGC 1410.

More perplexing to astronomers is that NGC 1409 is seemingly unaware that it is gobbling up a steady flow of material. A stream of matter funneling into the galaxy should have fueled a burst of star birth. But astronomers don’t see it. They speculate that the gas flowing into NGC 1409 is too hot to gravitationally collapse and form stars.

Astronomers also believe that the pipeline itself may contribute to the star-forming draught. The pipeline, a pencil-thin, 500 light-year-wide string of material, is moving a mere 0.02 solar masses of matter a year.

They estimate that NGC 1409 has consumed only about a million solar masses of gas and dust, which is not enough material to spawn some of the star-forming regions seen in our Milky Way. The low amount means that there may not be enough material to ignite star birth in NGC 1409, either.

The glancing blow between the galaxies was enough, however, to toss stars deep into space and ignite a rash of star birth in NGC 1410. The arms of NGC 1410, an active, gas-rich spiral galaxy, are awash in blue, the signature color of star-forming regions. The bar of material bisecting the center of NGC 1409 also is a typical byproduct of galaxy collisions.

Astronomers expect more fireworks to come. The galaxies are doomed to continue their game of “bumper cars,” hitting each other and moving apart several times until finally merging in another 200 million years.

NGC 1409 and NGC 1410 are both classified as a Seyfert II galaxies: galaxies with extremely bright nuclei that produce spectral line emission from highly ionized gas. The centers of Seyfert II galaxies have active galactic nuclei (AGN), and usually contain supermassive black holes with masses between 10 and 100 million solar masses. Their spectra show only narrow emission lines, in contrast to Seyfert I galaxies that show both narrow and broad lines.

This visible-light image is taken on October 25, 1999 with the the Space Telescope Imaging Spectrograph onboard the Hubble telescope, using three different color filters (red, green and blue), and represents the clearest view of how some interacting galaxies dump material onto their companions.

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