Scientists have known about a huge halo of gas around the Andromeda galaxy. But, the Hubble Telescope shows us it’s much bigger than we previously thought. NASA says this halo is six times larger and 1,000 times more massive than previous measurements indicated.

“Halos are the gaseous atmospheres of galaxies. The properties of these gaseous halos control the rate at which stars form in galaxies according to models of galaxy formation,” said Nicolas Lehner, the lead investigator, and an astrophysicist at the University of Notre Dame.

The halo is too dark for scientists to observe it directly. Instead, they looked for bright background objects through the gas to see how the light changed. Quasars were the perfect object to look for. 18 quasars were used in total to see the distribution of the gas.

This image from NASA perfectly shows how they used quasars to spot the halo. You can see how the dips in brightness correspond with where the halo is.

Andromeda galaxy halo

What about other galaxies? Hubble has studied 44 galaxies under the Hubble Cosmic Origins Spectrograph (COS) – Halos program. But, one problem always popped up. Only one quasar could be detected behind these galaxies. That gives scientists just one data point to try and map the size and structure of the halo in these faraway galaxies.

Andromeda was perfect because of its relative proximity to Earth. Several quasars were detected behind the galaxy and allowed scientists to develop a detailed map of the halo.

“This is a new milestone because typically only one quasar is used to probe the halos of galaxies beyond the Local Group,” said Lehner. “Here we have assembled a large sample of quasars that directly demonstrate the true extent of the halo of a single massive galaxy.”

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NASA touches on the origins of the halo in a press release:

But where did the giant halo come from? Large-scale simulations of galaxies suggest that the halo formed at the same time as the rest of Andromeda. The team also determined that it is enriched in elements much heavier than hydrogen and helium, and the only way to get these heavy elements is from exploding stars called supernovae. The supernovae erupt in Andromeda’s star-filled disk and violently blow these heavier elements far out into space. Over Andromeda’s lifetime, nearly half of all the heavy elements made by its stars have been expelled far beyond the galaxy’s 200,000 light-year diameter stellar disk.

What if Andromeda’s halo could be seen with the naked eye? NASA says if you held two basketballs at arm’s length – it would cover that much of the sky.

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The Hubble stays busy.

On May 5th, an international team of astronomers spotted a galaxy more than 13 billion years away. That means we are looking at light emitted when the galaxy was just 5% of its current age. Earth wasn’t even on the radar when this luminous galaxy was around.

oldest galaxy discovered

This galaxy?

spiral galaxy hubble

NGC 949 was first discovered in 1786 by Sir William Herschel. You can’t tell in the image above, but NASA is sure it’s a disk galaxy of some sort. Probably a spiral galaxy.

Image credits: NASA

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