Our home galaxy – the Milky Way – was "weighed accurately" for the first time, and it is surprisingly heavy.
An innovative study found that it was about 1.5 trillion times (1.5 billion billion times) more than the Sun.
Experts have been trying to measure the weight of the Milky Way for years, but it's hard work.
The main blocking point is "dark matter," a hypothetical hypothesis that science says must exist – but there is no way to see it directly.
This is why the previous estimates of the weight of the Milky Way have been widely shared – ranging from 500 billion to 3 billion solar masses (the mass of the Sun).
"We can not detect dark matter directly," said Laura Watkins of the Southern European Observatory, who led the team.
"That's what leads to the current uncertainty in the mass of the Milky Way – you can not accurately measure what you can not see."
But a new revolutionary weighing technique generates a total mass that takes into account dark matter. This is convenient because it represents about 90% of the mass of the Milky Way.
A single solar mass weighs 2 x 10 for a power of 30 kilograms, or 2,000,000,000,000,000,000,000,000,000 kg.
But the Milky Way weighs 1.5 trillion times that mass, which represents about 3 trillion.
Scientists have been able to calculate this astronomical number by measuring the velocity of globular clusters – dense groups of stars orbiting the spiral disk of the Milky Way.
"The more massive a galaxy, the faster its clusters move under the weight of its gravity," said N. Wyn Evans, of the University of Cambridge.
"Most of the previous measurements have revealed the speed with which a group approaches the Earth or retreats, that is, the speed along our line of sight.
"However, we have also been able to measure the lateral movement of the clusters, from which the total velocity, and hence the galactic mass, can be calculated."
By combining data from NASA's Hubble Space Telescope and ESA's Gaia Space Observatory.
These data revealed how objects moved in the Milky Way, allowing for very accurate measurements.
"Global groups extend over a large distance, so they are considered the best tracers used by astronomers to measure the mass of our galaxy," said Tony Sohn, of the Space Telescope Science Institute, who led Hubble measurements.
Roeland P. van der Marel, who also works at the Space Telescope Science Institute, added: "We were fortunate to have such a good combination of data.
"By combining Gaia measurements of 34 globular clusters with measurements from 12 clusters further away from Hubble, we could determine the mass of the Milky Way in a way that would be impossible without these two space telescopes."
Now that scientists know the mass of the Milky Way, it will be easier to perform other precise cosmological measurements.
At the end of last year, scientists have successfully measured all the stellar light ever produced in the observable universe.
This includes not only the current light of the stars, but all the light of the stars "produced during the history of the observable universe" – so it is a rather large number .
After all, our universe would be about 13.7 billion years old and began to form stars in a few hundred million years.
The best guess of science is that there are about two trillion galaxies and a trillion star.
Clemons College of Science astrophysicists used data from the NASA Fermi gamma ray telescope to determine the number of photons (light particles) ever produced by stars.
Technically, the number is known as septenvigintillion – also known as: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 000 000.
Yes, that's the number of photons that make up all the starlight ever produced in the observable universe, according to scientists writing in the journal Science.
On the other hand, it is estimated that the number of grains of sand on Earth is about 7.5 x 10 times the power of 18, or 7 500 000 000 000 000 000.
And the amount of water molecules on Earth is estimated at 4.6 x 10, for a power of 43, or 46, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000 000 000 000 molecules.
Basically, there is a lot of light.
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Are you surprised by the weight of the Milky Way? Let us know in the comments!
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