Our Lightweight Galaxy

[DrLeftover]

The Milky Way is lighter than astronomers previously thought, researchers have concluded.

A team of scientists led by the University of Edinburgh found it has about half the mass of a neighbouring galaxy, known as Andromeda.

Their estimates come from working out the mass of invisible matter found in the outer regions of both galaxies.

They concluded that dark matter accounted for Andromeda's extra weight.

Dark matter is a little-understood invisible substance which makes up most of the outer regions of galaxies.

The researchers have estimated that Andromeda contains twice as much dark matter as the Milky Way, causing it to be twice as heavy.

http://www.bbc.com/news/uk-scotland-28545437

 

[Evil Eye]

Cue fat shaming?


Sometimes I wonder how they arrive at conclusions like these when all they've got to go on is light/radiation

 

[Phazite]

There is quite a lot that be learned from light. In fact, I think it's fair to say that the study of light is what brought about the quantum theory and the theory of relativity. For being simply one branch of physics, there are entire colleges and university departments focused on the study of optics, such as the College of Optical Science at the University of Arizona. Just for your information, Wikipedia defines optics as so:

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

Some useful properties of light for gathering astronomical include frequency (color), intensity, and polarization. By measuring the spectrum of a star, astronomers can determine:

• Chemical composition - by analyzing the spectrum for absorption or emission bands
• Temperature - using Plank's law of black body radiation
• Angular and radial velocity - using the Doppler effect

(links go to Google image search)

There are many ways to measure distance. For nearby stars, we can use parallax to measure the change in position relative to the background of distant stars over the course of a year. If the type of star is know from its behavior and spectral properties, a Hertzsprung-Russell diagram can be used to calibrate the star's brightness to its distance. (Click for pretty HR diagram )

To measure the mass of a star, its motion can be observed and Kepler's laws can be applied. The same method can be used to determine the mass of star clusters and galaxies as well. Mass also be estimated based on the star's type and brightness.

Sorry to throw out a bunch of info, but it's incredibly amazing to me that so much can be known about the universe merely by measuring and studying light!

By the way, 2015 will be the "International Year of Light."