From the smallest microbe to the strongest oak, death is as true for above as it is below, even for the most powerful galaxies.
However, the process is not a quick one. A new haunting Hubble photograph of the 1947 NGC galaxy demonstrates this well: even from a distance of about 45.4 million light-years away (in the southern constellation of Dorado), we can see that the galaxy is slowly declining.
The clue is in dust and gas. A galaxy at the peak of its life will be filled with things, using it to create new stars. Eventually, star things will run out, and that’s what astronomers we see with NGC 1947 believe.
It is a rare type of galaxy known as a lenticular galaxy – disk-shaped, like the Milky Way or Andromeda, but without spiral arms. NGC 1947 used to have spiral arms, but consumed almost all the gas and dust that gave them structure; all that remains are a few screws, illuminated by the light of the stars.
(ESA / Hubble and NASA, D. Rosario; L. Shatz)
Galaxies that have not created new stars in billions of years are considered dead – but the Universe is not old enough for us to see what happens once all these stars die.
What about our galaxy? In fact, the Milky Way could have died at least once about 7 billion years ago; it revived after a period of 2 billion years, during which time a whole bunch of stars died, the supernova going and throwing its outer envelopes into space, filling the galaxy with material to create new stars.
The Milky Way currently has a relatively slow star formation rate of about 1 to 2 solar masses per year, but it also does not harm the new material. Our galaxy is a cannibal, with a history of the absorption of other galaxies and their entire wonderful star-forming material over its lifetime of 13.5 billion years, and is far from complete.
Eventually, the Magellanic Clouds will be hit on the Milky Way and we are heading for a merger with the Andromeda Galaxy in a few billion years. This could trigger a period of high star formation, as tidal interactions shock and compress the material in both galaxies.
Based on space observations around NGC 1947, an injection of fresh material from a fusion with another galaxy is unlikely, at least soon. It will continue to fade until only a raft of dead stars remains.
You can download the full-size versions of this image from the ESA website.