Hubble and Gaia accurately weigh the Milky Way

Hubble & Gaia accurately weigh the Milky Way
This artist's impression shows a computer generated model of the Milky Way and the accurate positions of the globular clusters used in this study surrounding it. Credit: ESA/Hubble, NASA, L. Calçada

In a striking example of multi-mission astronomy, measurements from the NASA/ESA Hubble Space Telescope and the ESA Gaia mission have been combined to improve the estimate of the mass of our home galaxy the Milky Way: 1.5 trillion solar masses.

The of the Milky Way is one of the most fundamental measurements astronomers can make about our galactic home. However, despite decades of intense effort, even the best available estimates of the Milky Way's mass disagree wildly. Now, by combining from the European Space Agency (ESA) Gaia mission with observations made with the NASA/ESA Hubble Space Telescope, astronomers have found that the Milky Way weighs in at about 1.5 trillion within a radius of 129 000 light-years from the galactic centre.

Previous estimates of the mass of the Milky way ranged from 500 billion to 3 trillion times the mass of the Sun. This huge uncertainty arose primarily from the different methods used for measuring the distribution of dark matter—which makes up about 90% of the mass of the galaxy.

"We just can't detect dark matter directly," explains Laura Watkins (European Southern Observatory, Germany), who led the team performing the analysis. "That's what leads to the present uncertainty in the Milky Way's mass—you can't measure accurately what you can't see!"

Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters—dense star clusters that orbit the spiral disc of the galaxy at great distances.

"The more massive a galaxy, the faster its clusters move under the pull of its gravity" explains N. Wyn Evans (University of Cambridge, UK). "Most previous measurements have found the speed at which a is approaching or receding from Earth, that is the velocity along our line of sight. However, we were able to also measure the sideways motion of the clusters, from which the total velocity, and consequently the galactic mass, can be calculated."

The group used Gaia's second data release as a basis for their study. Gaia was designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and to track their motions. Its second data release includes measurements of globular clusters as far as 65 000 light-years from Earth.

"Global clusters extend out to a great distance, so they are considered the best tracers astronomers use to measure the mass of our galaxy" said Tony Sohn (Space Telescope Science Institute, USA), who led the Hubble measurements.

The team combined these data with Hubble's unparalleled sensitivity and observational legacy. Observations from Hubble allowed faint and distant globular clusters, as far as 130 000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

"We were lucky to have such a great combination of data," explained Roeland P. van der Marel (Space Telescope Science Institute, USA). "By combining Gaia's measurements of 34 globular clusters with measurements of 12 more distant clusters from Hubble, we could pin down the Milky Way's mass in a way that would be impossible without these two space telescopes."

Until now, not knowing the precise mass of the Milky Way has presented a problem for attempts to answer a lot of cosmological questions. The content of a galaxy and its distribution are intrinsically linked to the formation and growth of structures in the Universe. Accurately determining the mass for the Milky Way gives us a clearer understanding of where our galaxy sits in a cosmological context.

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Citation: Hubble and Gaia accurately weigh the Milky Way (2019, March 7) retrieved 15 September 2019 from
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Mar 07, 2019
"Global clusters ..." said Tony Sohn
Did he really say that? Or did he say "globular clusters" and get his words mangled by a spell checker?

Mar 07, 2019
He actually said Gobble nut clusters, but the author couldn't tell the difference because he/she is an art history major.

Mar 08, 2019
The article should include a disclaimer, stating that the mass is the apparent mass based on the velocities they have measured. Because 90% of the mass is still imaginary (unproven DM). Either the mass is there, or else gravity or something else needs to be re-evaluated.

Mar 08, 2019
It does not help much to measure the 3-D movement components of mass objects in a local energy frame as 'mass' is just a book-keeping tool to observe 'matter' or motion and gravitationally energized mass. By far, the most dominant energy component comes from the motion of any mass object in 3-D space along the invisible orthogonal direction of Riemann 4-sphere. Local 4-D motion components (including kinetic energy and DM or mass waves of unstructured matter) are balanced by the decelerating pull of gravitational energy of all other mass objects in universe, see the vast literature since 1995 of the unified GR/QM theory of Suntola Dynamic Universe. It has already resolved the problems of DE/DM.

Mar 08, 2019
It has already resolved the problems of DE/DM.

I must have missed the Nobel physics awards that year.

Mar 08, 2019
No C, the Nobel Committee did "not" miss.
They were laughing so hard,
so loudly!
That the wooloons finally gave up & sulked out of the building.

Mar 09, 2019
It used to take decades to get a Nobel for an invention such as the DU explanation of SN1a 1998 data. History is measured in thousands of years for a major paradigm change from Ptolemy Earth to Sun centered universe and some 400-500 years from Copernicus/Galileo/Kepler/Leibniz and Newton period to math physicists and the GR/QM era. Einstein wasted 30 yrs of his life in search of the unified theory. Feynman in 1960's was getting close to the DU energy balance principle but could not open the Planck energy equation (of structured and unstructured mass-waves) to the required m C4 C form of SR/GR. Suntola break-through in 1995 explained why only the local APPARENT speed of light C is observed constant but the TRUE values of C=C4 are decelerating - resulting in 5-10 blunders in GR/QM and SN1a model of GR. rrMousie is laughing at the hasty 2011 Nobel blessing of GR based DE of accelerated vs decelerating expansion and will likely gulp JD invented youghoord into lungs after DU based DE award.

Mar 23, 2019
rrGulpy, you are safe - the yoghoord wooloon finally gave up and sulked out of building changing to plan C of astro-charmer youghoord label, take care rr and look out what yoghurt j'are gulping after DU based DE award or offer it to 2011 Nobel committee!

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