Swapna Krishna

Dec 8th 2021

An X-Ray of the Sky Shows Us More Than Ever


There’s still a lot we don’t know about the universe around us. One way scientists and researchers gain new information about the vast cosmos and our place within it is by taking an image of the galaxy. The Hubble Deep Field images are some of the most popular examples of this type of work.

The first of these extraordinary pictures was taken by pointing Hubble at one part of space for 10 consecutive days to see how far the telescope could see. Over the course of 100-plus exposure hours, it took 342 separate images, which became the first Hubble Deep Field picture. Thanks to Deep Field, scientists have been able to look at the most distant galaxies we’ve ever been able to see.

More recently, scientists using the German-Russian eROSITA telescope took X-rays of the sky, peering deeper into the cosmos than any other similar images before it. Rather than looking deep into one part of space, like Hubble Deep Field, the eROSITA X-ray is a full sweep of the entire sky, and it uncovers quite a bit we didn’t know previously about the nature of the hot, energetic universe around us.

How eROSITA Took This Amazing Photograph

eROSITA is a space-based X-ray telescope that’s part of the Spectrum-Roentgen-Gamma (SRG) mission, which is located at the L2 Lagrange point in space — close enough to maintain contact with Earth but far enough away to provide a deep, clear view into space, as NASA explains. This full-sky survey of X-rays was taken over the course of six months and completed on June 11, 2020. It’s the first of eight sky surveys planned for the eROSITA telescope.

To ensure the exposures would be even, the telescope was rotated constantly. Researchers then projected the data that eROSITA sent back about the sky, around 165 gigabytes so far, onto an ellipse, with the center of our galaxy in the middle of the image and the Milky Way’s body across the horizontal plane.

Decoding eROSITA’s Image of the Galaxy

These incredible X-rays from eROSITA have already changed the way scientists view the galaxy. The image of the galaxy uncovered 1.1 million sources of X-ray within the known universe, which doubled what scientists previously had on record, according to Science News. Researchers color-coded the image according to the amount of energy produced: Blue indicates the highest-energy areas, then green, then yellow and, finally, red.

“This all-sky image completely changes the way we look at the energetic universe,” said Peter Predehl, principal investigator of eROSITA, in a Max Planck Institute for Extraterrestrial Physics (MPE) press release. “We see such a wealth of detail — the beauty of the images is really stunning.”

One discovery that the eROSITA X-rays have already made is the presence of mysterious giant bubbles that seem to be coming from the center of the Milky Way galaxy, Space reports. These bubbles are similar to the Fermi bubbles, which are formed of hot, highly energized gamma rays. However, the eROSITA bubbles are comparatively less energetic and less hot. This is just one of the cosmological mysteries scientists can now decode thanks to the light eROSITA has shed on the universe’s phenomena.

The eROSITA image isn’t just limited to our galaxy, though; scientists are able to see supermassive black holes at the center of other galaxies (the highest, most active energies that eROSITA was able to detect) that are up to a billion light-years away. Studying extremely distant galaxies is a chance to peer back in time and see how our early universe looked.

Where Do We Go From Here?

According to MPE, eROSITA will be studying the sky for at least the next three and a half years (hopefully longer) in the pursuit of scientists understanding dark energy, the invisible force that’s driving our universe’s expansion.

“The SRG Observatory is now starting its second all-sky survey, which will be completed by the end of this year,” said Rashid Sunyaev, lead scientist of the Russian SRG team, in the MPE press release. “Overall, during the next 3.5 years, we plan to get 7 maps similar to the one seen in this beautiful image. Their combined sensitivity will be a factor of 5 better and will be used by astrophysicists and cosmologists for decades.”

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