Astronomers calculate the mass of the entire Milky Way galaxy

How heavy is the Milky Way galaxy? It may seem impossible to get a sense of it from our tiny little planet, but astronomers have their ways. Now a team has used data from Hubble and the Gaia satellite to make the most accurate measurement yet of the mass of the galaxy by studying the motions of star clusters orbiting the Milky Way.

more…

Tau.Neutrino said:

Astronomers calculate the mass of the entire Milky Way galaxy

How heavy is the Milky Way galaxy? It may seem impossible to get a sense of it from our tiny little planet, but astronomers have their ways. Now a team has used data from Hubble and the Gaia satellite to make the most accurate measurement yet of the mass of the galaxy by studying the motions of star clusters orbiting the Milky Way.

more…

Oh good. It used to be extremely inaccurate because of the unknown mass ot the outer part of the dark matter halo. The only way to determine this was to track the orbital motion of the dwarf satellite galaxies orbiting the Milky Way.

But now, both this and stars in the outer halo should be able to be used together.

mollwollfumble said:

Tau.Neutrino said:

Astronomers calculate the mass of the entire Milky Way galaxy

How heavy is the Milky Way galaxy? It may seem impossible to get a sense of it from our tiny little planet, but astronomers have their ways. Now a team has used data from Hubble and the Gaia satellite to make the most accurate measurement yet of the mass of the galaxy by studying the motions of star clusters orbiting the Milky Way.

more…

Oh good. It used to be extremely inaccurate because of the unknown mass ot the outer part of the dark matter halo. The only way to determine this was to track the orbital motion of the dwarf satellite galaxies orbiting the Milky Way.

But now, both this and stars in the outer halo should be able to be used together.

> 1.5 trillion solar masses. In the grand scheme of things, that makes the Milky Way kind of an upper-middle mass galaxy.

Good.

> In this case, the objects in question are globular clusters – ancient bunches of stars that orbit the Milky Way.

Assuming they are far enough away from the Milky Way centre?

> The researchers examined Gaia measurements of 34 globular clusters as far as 65,000 light-years away, along with Hubble data on 12 clusters up to 130,000 light-years away. By combining these into anchor points, the team was able to estimate the distribution of the Milky Way’s mass, extending out to almost 1 million light-years from Earth.

Same question. How do you get from that into the region between 130,000 and 1 million light years?

Um, what’s the title of the original technical article?

mollwollfumble said:

mollwollfumble said:

Tau.Neutrino said:

Astronomers calculate the mass of the entire Milky Way galaxy

How heavy is the Milky Way galaxy? It may seem impossible to get a sense of it from our tiny little planet, but astronomers have their ways. Now a team has used data from Hubble and the Gaia satellite to make the most accurate measurement yet of the mass of the galaxy by studying the motions of star clusters orbiting the Milky Way.

more…

Oh good. It used to be extremely inaccurate because of the unknown mass ot the outer part of the dark matter halo. The only way to determine this was to track the orbital motion of the dwarf satellite galaxies orbiting the Milky Way.

But now, both this and stars in the outer halo should be able to be used together.

> 1.5 trillion solar masses. In the grand scheme of things, that makes the Milky Way kind of an upper-middle mass galaxy.

Good.

> In this case, the objects in question are globular clusters – ancient bunches of stars that orbit the Milky Way.

Assuming they are far enough away from the Milky Way centre?

> The researchers examined Gaia measurements of 34 globular clusters as far as 65,000 light-years away, along with Hubble data on 12 clusters up to 130,000 light-years away. By combining these into anchor points, the team was able to estimate the distribution of the Milky Way’s mass, extending out to almost 1 million light-years from Earth.

Same question. How do you get from that into the region between 130,000 and 1 million light years?

Um, what’s the title of the original technical article?

Why are they stretching it out to 1 million light years for?

Is that based on particles per square meter in space around it?

Tau.Neutrino said:

mollwollfumble said:

mollwollfumble said:

Oh good. It used to be extremely inaccurate because of the unknown mass ot the outer part of the dark matter halo. The only way to determine this was to track the orbital motion of the dwarf satellite galaxies orbiting the Milky Way.

But now, both this and stars in the outer halo should be able to be used together.

> 1.5 trillion solar masses. In the grand scheme of things, that makes the Milky Way kind of an upper-middle mass galaxy.

Good.

> In this case, the objects in question are globular clusters – ancient bunches of stars that orbit the Milky Way.

Assuming they are far enough away from the Milky Way centre?

> The researchers examined Gaia measurements of 34 globular clusters as far as 65,000 light-years away, along with Hubble data on 12 clusters up to 130,000 light-years away. By combining these into anchor points, the team was able to estimate the distribution of the Milky Way’s mass, extending out to almost 1 million light-years from Earth.

Same question. How do you get from that into the region between 130,000 and 1 million light years?

Um, what’s the title of the original technical article?

Why are they stretching it out to 1 million light years for?

Is that based on particles per square meter in space around it?

It’s based on density of dark matter. The dark matter density is still very high as far out as the stars reach.

https://en.wikipedia.org/wiki/Dark_matter_halo#Density_profiles

A commonly used model for galactic dark matter halos is the pseudo-isothermal halo, but that gives the Milky Way an infinite mass, which is not realistic.

Numerical simulations of structure formation in an expanding universe lead to the theoretical prediction of the NFW dark matter density profile. This still gives the Milky Way an infinite mass.

See the wikipedia link for the fudge used to turn the Milky Way from an infinite mass object to a finite mass object. It involves arbitrarily truncating the dark matter halo at a specific density.

mollwollfumble said:

It’s based on density of dark matter. The dark matter density is still very high as far out as the stars reach.

https://en.wikipedia.org/wiki/Dark_matter_halo#Density_profiles

A commonly used model for galactic dark matter halos is the pseudo-isothermal halo, but that gives the Milky Way an infinite mass, which is not realistic.

Numerical simulations of structure formation in an expanding universe lead to the theoretical prediction of the NFW dark matter density profile. This still gives the Milky Way an infinite mass.

See the wikipedia link for the fudge used to turn the Milky Way from an infinite mass object to a finite mass object. It involves arbitrarily truncating the dark matter halo at a specific density.

From TATE:

“This provides a good fit to most rotation curve data. However, it cannot be a complete description, as the enclosed mass fails to converge to a finite value as the radius tends to infinity. “

Why shouldn’t the mass be infinite if the radius is infinite?