what is the mass of our galaxy?

Answer 1

it seems the mass estimate is between 600 000 000 000 (six hundred billion) to 300 000 000 000 000 (three hundred trillion) solar masses.

look here
http://en.wikipedia.org/wiki/Milky_Way#Structure

Answer 2

Estimates range between 200 and 600 billion solar mass.

How is it determined? By how fast satellite galaxies orbit (yes, there is such a thing as "moon" galaxies. The small Magellanic cloud and the large Magellanic cloud are two dwarf galaxies orbiting around the Milky Way) and how quickly the galaxy spins on its axis. Which is very hard to measure and is subject to consideration of "missing mass" (galaxies behave like if there was more mass than the mass of star -- linked with how much light they put out -- would suggest.

Answer 3

The latest estimates for the visible mass of the Galaxy are 600-750 billion solar masses and the overall mass is ~2 trillion solar masses, possibly somewhat higher. It's the most massive member of the Local Group.

Latest estimates for the Andromeda Galaxy are:

visible = 300-400 billion solar masses

overall = 1.2 trillion solar masses

Answer 4

MASS of our galaxy is roughly 100 billion times the mass of the Sun

By measuring the total amount of light in the galaxy (called luminosity), and knowing the mass, one can estimate the number of stars that are there in the galaxy. So, even though we cannot actually count the number of stars in the galaxy, we can estimate the number of stars in the galaxy as roughly 100 billion (100,000,000,000). It turns out that there are many more stars with mass less than the mass of the Sun than with mass more than the mass of the Sun. So, it all works out right..

Answer 5

The mass contained in the Milky Way (in the visible disk) is 2x10^11 M(Sun), or 200,000,000,000 solar masses. That's 200 trillion solar masses.

The mass contained in the Milky Way galaxy (out to as far as we can see Hydorgen-I gas) is 6x10^11 M(Sun), or 600,000,000,000 solar masses. Six hundred trillion solar masses.

It should be noted that our galaxy contains about 100 billion suns, so you can deduce that may suns in our galaxy have a mass greater than the mass of our sun.

Answer 6

Mass of the Milky Way Galaxy

The mass of an object is one of the most fundamental properties of the object. As such, reliable ways to measure mass are exceedingly important.

One way is to simply measure the optical emission (luminosity of a galaxy) and to (independently) determine the average mass of a star in the galaxy. This will then lead to an estimate for the mass of the galaxy if all of the luminosity is in fact due to the stars and all material radiates in a similar manner. This method has problems because it is sometimes difficult to know whether all mass produces radiation.

Another way to determine masses is to use our knowledge of physics (in particular, gravity). Since all mass is expected to interact gravitationally whether or not we can see it, we should be able to measure the mass of objects even if they are invisible to our eyes by their effects on nearby objects. This is the tact we now pursue.

The gist of the method is to note that all objects are in orbit around the center of our Galaxy. To see how this allows us to infer the mass of our Galaxy, consider the Earth in its orbit in our Solar System.

The Earth is attracted to the Sun by the force of gravity. If the Earth were stationary, the force of gravity would draw the Earth into the Sun in less than 1 year and we would be gone.

The Earth overcomes this tendency by moving around the Sun with a speed such that the centrifugal force just balances the inward tug of gravity.

The mass of the Sun and Earth and the distance between the Earth and Sun determine the strength of the gravitational attraction. The speed of the Earth's motion and the distance of the Earth from the Sun determine the strength of the centrifugal force. For a given size orbit, the mass of the Sun determines how fast the Earth must move to stay in orbit. To turn this around, note that if we can measure how fast the Earth moves in its orbit and the size of its orbit, then we can infer the mass of the Sun! The simple expression for the mass of the Sun is

M(Sun) = v2D/G
where G is the gravitational constant, v is the orbital speed, and D is approximately the distance from the Earth to the Sun.

This is the basis of the method used to determine the mass of the Milky Way galaxy (and other disk galaxies). However, before we move on, we have one further tweak to consider.

A. In the Solar System, the planets orbit about the Sun. None of the planets orbit within the body of the Sun. The planets closer to the Sun feel stronger gravitational tugs due to the Sun and thus must travel faster to maintain their orbits. For example, the Earth travels with a speed of ~30 km per second. Pluto travels with a speed of ~4.6 km per second. This is typical of a sytem where bodies orbit outside of the attracting mass.
B & C. Suppose we lived in a spherical system where the mass was spread out and we orbited inside of the body. Newton showed that only the mass contained within our orbit contributed to the gravitational force on us. So, if we approached the center of the object, the gravitational force would, in general, vanish. In such an extended object, the orbital speed would not fall-off as quickly as one moved away from the center of the body and, in fact, the orbital speed could stay the same and could even increase in some cases.

For the Milky Way, we find that the orbital speed increases and then remains roughly constant. This implies that we are still within the body of the Milky Way, even at the largest distances from the center of the Milky Way. We have not yet located the edge of the Milky Way; the Milky Way extends much further than the edge of the disk of stars (the visible disk)!


The mass contained in the Milky Way (in the visible disk) is 2x1011 M(Sun).

the mass contained in the Milky Way galaxy (out to as far as we can see HI gas) is 6x1011 M(Sun).

Oh my, the mass where we can see stars is only 1/3 of the mass of the entire Galaxy. This suggests that a lot of mass in the Milky Way is in some form which does not radiate large amounts of light (Dark matter). This interesting result will keep popping up throughout the rest of the course as we discuss mass determinations for the Universe.

Answer 7

not sure they can prove anything in that