Milky Way Weighs 1.5 Trillion Suns and Most is Dark Matter

NASA’s Hubble Space Telescope and the European Space Agency’s Gaia satellite have more precisely weighed the Milky Way galaxy.

Above – On the left is a Hubble Space Telescope image of a portion of the globular star cluster NGC 5466. On the right, Hubble images taken ten years apart were compared to clock the cluster’s velocity. A grid in the background helps to illustrate the stellar motion in the foreground cluster (located 52,000 light-years away). Notice that background galaxies (top right of center, bottom left of center) do not appear to move because they are so much farther away, many millions of light-years.
Credits: NASA, ESA and S.T. Sohn and J. DePasquale (STScI)

The Milky Way weighs in at about 1.5 trillion solar masses (one solar mass is the mass of our Sun), according to the latest measurements. Only a tiny percentage of this is attributed to the approximately 200 billion stars in the Milky Way and includes a 4-million-solar-mass supermassive black hole at the center. Most of the rest of the mass is locked up in dark matter, an invisible and mysterious substance that acts like scaffolding throughout the universe and keeps the stars in their galaxies.

Old estimates for our galaxy’s mass ranged between 500 billion to 3 trillion solar masses. The improved measurement is near the middle of this range.

The lightest galaxies are around a billion solar masses, while the heaviest are 30,000 times more massive.

The Hubble and Gaia observations are complementary. Gaia was exclusively designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and track their motions. It made exacting all-sky measurements that include many globular clusters. Hubble has a smaller field of view, but it can measure fainter stars and therefore reach more distant clusters. The new study augmented Gaia measurements for 34 globular clusters out to 65,000 light-years, with Hubble measurements of 12 clusters out to 130,000 light-years that were obtained from images taken over a 10-year period.

When the Gaia and Hubble measurements are combined as anchor points, like pins on a map, astronomers can estimate the distribution of the Milky Way’s mass out to nearly 1 million light-years from Earth.


Written By Brian Wang


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