section_path: Size and mass/Mass
section_name: Mass
paragraph_text: Mass
  
  The Milky Way is approximately 890 billion to 1.54 trillion times the mass of the Sun in total (8.9 × 10 to 1.54 × 10 solar masses), although stars and planets make up only a small part of this. Estimates of the mass of the Milky Way vary, depending upon the method and data used. The low end of the estimate range is 5.8 × 10 solar masses (M), somewhat less than that of the Andromeda Galaxy. Measurements using the Very Long Baseline Array in 2009 found velocities as large as 254 km/s (570,000 mph) for stars at the outer edge of the Milky Way.
  
  Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 × 10 M within 160,000 ly (49 kpc) of its center. In 2010, a measurement of the radial velocity of halo stars found that the mass enclosed within 80 kilo parsecs is 7 × 10 M. In a 2014 study, the mass of the entire Milky Way is estimated to be 8.5 × 10 M, but this is only half the mass of the Andromeda Galaxy. A recent 2019 mass estimate for the Milky Way is 1.29 × 10 M.
  
  Much of the mass of the Milky Way seems to be dark matter, an unknown and invisible form of matter that interacts gravitationally with ordinary matter. A dark matter halo is conjectured to spread out relatively uniformly to a distance beyond one hundred kiloparsecs (kpc) from the Galactic Center. Mathematical models of the Milky Way suggest that the mass of dark matter is 1–1.5 × 10 M. 2013 and 2014 studies indicate a range in mass, as large as 4.5 × 10 M and as small as 8 × 10 M. By comparison, the total mass of all the stars in the Milky Way is estimated to be between 4.6 × 10 M and 6.43 × 10 M.
  
  In addition to the stars, there is also interstellar gas, comprising 90% hydrogen and 10% helium by mass, with two thirds of the hydrogen found in the atomic form and the remaining one-third as molecular hydrogen. The mass of the Milky Way's interstellar gas is equal to between 10% and 15% of the total mass of its stars. Interstellar dust accounts for an additional 1% of the total mass of the gas.
  
  In March 2019, astronomers reported that the virial mass of the Milky Way Galaxy is 1.54 trillion solar masses within a radius of about 39.5 kpc (130,000 ly), over twice as much as was determined in earlier studies, suggesting that about 90% of the mass of the galaxy is dark matter.
  
  In September 2023, astronomers reported that the virial mass of the Milky Way Galaxy is only 2.06 10 solar masses, only a 10th of the mass of previous studies. The mass was determined from data of the Gaia spacecraft.