Radio Galaxies and Quasars

Powerful natural radio transmitters associated withGiant elliptical galaxies

Demo

How we know distances to radio galaxies: redshifts (Doppler shifts) + Hubble’s Law

The discovery of quasars: a history lesson that teaches something about the universe

Some of the brightest radio sources, 3C48, 3C273, did not seem to be associated with

galaxies, but with star-like objects

Spectra of quasars showed strong emission lines, highly redshifted

See Figure 24.2 of text

Application of Hubble’s Law indicates enormously distant,Brilliant objects. But where are the galaxies?

With Hubble Space Telescope, we have

imaged Quasars

What are quasars?

Artistic view of an early quasar

Physically what They are

Whether we see a radio galaxy or quasar depends on how we view them

In quasars and radio galaxies, there is a connection from the small to the extremely

large: M87

M87 at radio wavelengths: it exists on many scales

The “Central Engines” of quasars and radio galaxies: black holes of 1 - 10 billion

solar masses

Summary of Quasar Characteristics

• Clearly are a brilliant, energetic phenomenon in centers of galaxies

• Quasars are very distant. We see them as they were long ago

• Let’s look at the distribution of quasar redshifts

Question: what does this mean?

7236 quasars

Extragalactic Astronomy as a Time Machine

Observations of quasars and radio galaxies allow us to look out billions of light years

into space• NVSS survey of the sky at radio

wavelengths found 1.8 million sources, almost all of which are radio galaxies and quasars

• The Sloan Digital Sky Survey (SDSS) measured positions, brightness, and spectra (therefore distances) of 675,000 galaxies and 90,000 quasars

• What do we see? What is the shape of the universe as a whole?

Galactic filaments and voids

Figure 25.29 from book

Why are there filaments and voids in the distribution of galaxies?