Starbirth After the Inexorable Collision of Two Galaxies

Fagjun | Published 2017-10-11 21:21

The collision of two distinct galaxies has given rise to perfect conditions for starbirth.


An infant star surrounded by dust [Image by ESO/L. Calçada/M. Kornmesser]



The galaxy NGC 4490 and the smaller galaxy NGC 4485 have been skirting each other in a kind of gravitational tango for millions of years. A long time ago, the inevitable finally happened: the two galaxies collided, mixing together and creating the dense gases that birth stars. The Hubble Telescope caught images of the entwined galaxies, showing pink bursts of light that indicate regions where new stars are being born.


Astronomers say that the galaxies have now moved apart and past each other. However, because of gravity and their humongous mass, the two galaxies will collide with each once again at some point in the future.


Galaxy NGC 4490 has now earned the moniker “starburst galaxy” from astronomers due to the appearance of the birth of its new stars.



The Starbirth of the Past




Now, you may be wondering a little about the tenses in this article. If the galaxies have since moved away from each other, why are we still talking about the collision as if it's still happening? Here's the thing about observing objects far away from Earth—time gets a little muddled. Together, NGC 4490 and NGC 4485 form Arp 269, a system rightfully included in the Atlas of Peculiar Galaxies. This system is situated about 24 million light years away from Earth, in the Canes Venatici constellation. This means that the events that we're able to observe in our now has actually already happened 24 million years ago.


Galaxy NGC 4490, left, and the smaller NGC 4485 [Image by Adam Block/Mount Lemmon SkyCenter/University of Arizona]



Light is fast, but space is vast. Thus, the light from far away stars may only reach us long after that particular star has already dimmed or even died. So when we look at NGC 4490 and NGC 4485, we're looking at starbirth that occurred millions of years ago. For all we know, some of the stars we're watching get born have already died, or are already dimming. In fact, scientists have already detected supernovae in the two galaxies in recent years. It's entirely possible, therefore, that the stars we're seeing may have already exploded.


The collision of these two galaxies, the resulting starbirth, and the fact that it all happened tens of millions of years ago all make for a good crash course on how time works when it comes to objects millions of light years away from Earth.

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