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The peaceful-looking Umbrella Galaxy has a violent, cannibalistic past

The Hubble Space Telescope has captured another image of one of the strange and wondrous sights of our universe — this one showing the spiral galaxy NGC 4651, also known as the Umbrella Galaxy.

Although the galaxy “may look serene and peaceful as it swirls in the vast, silent emptiness of space,” Hubble astronomers write, “don’t be fooled — it keeps a violent secret. It is believed that this galaxy consumed another smaller galaxy to become the large and beautiful spiral that we observe today.”

It is thought that long ago, a smaller dwarf satellite galaxy orbited around a larger galaxy. But the dwarf galaxy came too close to its larger neighbor and was torn apart by gravitational forces, being absorbed into the larger galaxy.

The spiral galaxy NGC 4651, captured in by the Hubble Space Telescope in an image released on March 30, 2020.
The spiral galaxy NGC 4651, captured in by the Hubble Space Telescope in an image released on March 30, 2020. ESA/Hubble & NASA, D. Leonard

The galaxy today is known as the Umbrella Galaxy due to a faint umbrella-shaped structure that extends outward from the main body of the galaxy. That structure can’t be seen in this image, but it is clearly visible in this older image of the same galaxy. The enormous structure stretches 100,000 light-years out from the galactic disk, and is composed of the trails left behind by stripped stars.

The umbrella structure was formed as a result of this galaxy devouring its neighbor. As the smaller galaxy was torn apart by the gravitational forces in a process called gravitational stripping, it formed into a long, thin structure called a tidal stream. It is thought that these streams, composed of stars and gas, can eventually form extended disks, such as the one seen around the Andromeda galaxy. But in the case of the Umbrella Galaxy, the stream was pulled away from the main galactic disk and it eventually spread out to form the umbrella shape.

Another reason that the Umbrella Galaxy is notable is that it can be seen using amateur telescopes. As the Hubble scientists explained, “Although only a telescope like the NASA/ESA Hubble Space Telescope, which captured this image, could give us a picture this clear, NGC 4651 can also be observed with an amateur telescope — so if you have a telescope at home and a star-gazing eye, look out for this glittering carnivorous spiral.”

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