Milky Way weighs about 1.5 trillion solar masses

Milky Way's mass mostly made up of dark matter, new research into the galaxy reveals - 10-Mar-2019 - NZ International news

Milky Way's mass mostly made up of dark matter, new research into the galaxy reveals - 10-Mar-2019 - NZ International news

Now scientists have done just that, using new data from the Hubble Space Telescope combined with the Gaia spacecraft. The results are in: Our galaxy weighs about 1.54 trillion solar masses, according to a new study scheduled for publication in the Astrophysical Journal.

Previous estimates of the Milky Way's mass ranged from 500 billion to 3 trillion solar masses.

"Because of their great distances, globular star clusters are some of the best tracers astronomers have to measure the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk of stars", said Tony Sohn of STScI, who led the Hubble measurements. "That's what leads to the present uncertainty in the Milky Way's mass - you can't measure accurately what you can't see". The faster the clusters move, the more massive the galaxy.

Scientists have previously been able to measure the speed at which a globular cluster approaches or recedes from Earth along our line of sight but this information alone is quite limiting.

Variation comes from disagreements and discrepancies in techniques used to measure and weigh dark matter, which make sup to 90 per cent of the galaxy. "With this method, we can measure the total mass of everything inside the Milky Way (the dark matter, gas, stars, planets, black holes), all added together". Gaia was specially designed to create a precise 3-dimensional map of astronomical objects throughout the Milky Way and track their motions and made challenging all-sky measurements that included several globular clusters. Due to their great distances, globular star clusters allow astronomers to trace the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk.

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The project involved global collaboration between scientists working for NASA and ESA on the Hubble and Gaia telescopes. "We could pin down the Milky Way's mass in a way that would be impossible without these two space telescopes".

Hanging over the scruff of Ursa Major's neck some 12 million light-years from Earth, a cluster of young stars known as the Cigar Galaxy is puffing epic amounts of wind into deep space. That means there's a pretty large margin of error in the estimate, meaning the true mass of the Milky Way may be somewhere between 0.79 and 2.29 trillion solar masses-but the current estimate is a good start. So the team looked at 34 distant clusters measured over 22 months by ESA's Gaia star survey satellite ranging from 6,500 to 70,000 light years away. "The Milky Way is the closest galaxy to us so it is the one we can study in most detail". Since Hubble has been observing some of these objects for ten years, it was also possible to accurately track the velocities of these clusters as well. Gaia was launched on 19 December 2013 and is located at the L2 Lagrange point - the same location that the upcoming NASA/ESA/CSA James Webb Space Telescope will have.

If you have ever been to a school fete and seen a large, glass jar filled with candies, labelled "guess how many jelly beans there are", chances are you have studied it meticulously to try and work out that magic number.

The mass of the Milky Way is one of the most fundamental measurements astronomers can make about our galactic home. "We're inside the Milky Way, stuck about halfway out from the center, and everything we learn about it we learn from right here".

Roeland P. van der Marel of the Space Telescope Science Institute calls the team lucky for having access to informative data from two different sources.

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