Dark Matter, Dark Energy, and the Fate of the Universe

3 Pages
87 Views

Department
Astronomy
Course Code
ASTRON 100
Professor
Alexandra Pope

This preview shows page 1. Sign up to view the full 3 pages of the document.
Description
Dark Matter, Dark Energy, and the Fate of the Universe Names given to unseen influences ● Dark Matter: an undetected form of mass that emits little or no light, but whose existence we infer from its gravitational influence. ● Dark Energy:An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate. Contents of Universe ● “Ordinary” Matter”: ~ 4.4% ○ Ordinary matter inside stars: ~ 0.6% ○ Ordinary matter outside stars: ~ 3.8% ● Dark Matter: ~ 23% ● Dark Energy: ~ 73% What is the evidence for dark matter in galaxies? ● We measure the mass of the solar system using the orbits of planets: ○ Orbital Period ○ Average Distance ● For circles: ○ Orbital velocity ○ Orbital radius Rotation Curve ● Aplot of orbital velocity versus orbital radius. ● The solar system’s rotation curve declines because the Sun has almost all the mass. ● The rotation curve orbital velocity rises with radius. ● The rotation curve of the Milky Way stays flat with distance. ● Mass must be more spread out than in the solar system. ● Mass in the Milky Way is spread out over a larger region than its stars. ● Most of the Milky Way’s mass seems to be dark matter. ● Mass within the Sun’s orbit: ○ 1.0 x 10^11 Msun ● Total mass of the Milky Way: ○ ~10^12 Msun ● The visible portion of the galaxy lies deep in the heart of a large halo of dark matter. How do we measure the rotation in other galaxies? ● We can measure the rotation curves of other spiral galaxies using the Doppler shift of the 21-cm line of atomic hydrogen. ● Spiral galaxies all tend to have flat rotation curves, indicating large amounts of dark matter. ● Spiral galaxies: 10% visible matter + 90% dark matter ● Broadening of spectral lines in elliptical galaxies tells us how fast the stars are orbiting. ● These galaxies also have dark matter. Evidence for dark matter in clusters of galaxies: galaxies velocities ● We can measure the velocities of galaxies in a cluster from their Doppler shifts. ● Broadening of spectral lines in elliptical galaxies tells us how fast the stars are orbiting. ● These galaxies also have dark matter. ● The mass we find from galaxy motions in a cluster about 50 times larger than the mass in stars. Evidence for dark matter in clusters of galaxies: Hot Gas ● Clusters contain large amounts of X-ray emitting hot gas. ● Temperature of hot gas tells us the particle motions which tells us cluster mass: ○ 85% dark matter ○ 13% hot gas ○ 2% stars Evidence for dark matter in clusters of galaxies: Gravitational Lensing ● Gravitational lensing, the bending of light rays by gravity, can also tell us a cluster’s mass. All three methods
More Less
Unlock Document

Only page 1 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit