Galaxies

Origin of the , Tintoretto

Peter Watson, Dept. of Physics Peter Watson

First: some things that •e.g. M3 (note lots of red giants) aren’t galaxies • A lot of the Messier objects are globular clusters of : relatively bright and close, mostly old stars • e.g. M2 in Aquarius: about 100000 stars

Credit & Copyright: D. Williams, N. A. Sharp, AURA, NOAO, NSF

Peter Watson Peter Watson

Anglo-Australian Telescope photograph by David Malin •~200 round our : Copyright: Anglo-Australian Telescope Board •Dynamics are easy to understand all galaxies seem to have them.

•M87 (more about it later) has about 1000 globulars.

Peter Watson Peter Watson Spiral Galaxies • Some are tightly wound up,like M31 (the )

• Some are spread out, like NGC6946

• About 10 billion stars

• About 100,000 light years across

• Can’t see individual stars: red patches are “ nurseries”

• “Hot spot” in centre

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• Some have “bars” across the centre

•Some are seen side on

•NGC4565

•Note the dust clouds

Peter Watson Peter Watson

M101 aka Pinwheel As usual, see a lot more if we look at them in different ways

Peter Watson Peter Watson Why spirals? • Purple =x-rays • spiral arms are young new • Blue = UV stars • Yellow = optical • old stars don’t show arms • Red = IR • Note rotation of galaxy ~ 500 • Note arms seem million years to be hot, means young • lifetime of large stars ~ 10 stars million • Density wave theory Peter Watson

Why spirals? The Milky Way is hard to see, since we are inside it! Group of young stars • But it looks roughly like this

go supernova • With the about here and compress gas

small stars remain, new group of young stars are born

Peter Watson

If you are in Scotland The centre of the Milky Way • Go to the Crawick multiverse • This is the Milky way, showing the whole sky M31 (Andromeda) • Site of old open pit mine Milky Way

Peter Watson • we can pick out the same general structure in radio waves, but note very intense source •And gamma-rays at centre

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Galactic Centre • •But we can zoom in with radio waves Not visible directly (too much dust)

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•And X-rays The stars there are swirling round something~1000000 Mo

Peter Watson Peter Watson •In addition to the stars, there is a huge clump •Something like this! of gas feeding it

Peter Watson Peter Watson

Whole picture is consistent with massive black • •Some galaxies have grabbed hold of other galaxies hole (4 million xMo) at centre •This is M51 •Can see this in other galaxies

Peter Watson Peter Watson

Elliptical galaxies are much •Then there are galaxies that seem to less fun! having problems:

• NGC 1512

• : stars NGC 4881 are forming in huge in Coma numbers round the outside

Credit: W. A. Baum (U. Washington), WFPC2, HST, NASA

Peter Watson Peter Watson M87 looks dull And it has a huge jet But it’s huge: one trillion stars emerging from the black hole at its centre

Which seems more complicated the closer you look!

Peter Watson Peter Watson

Centaurus A is a strange Sometimes the jets are far galaxy larger than the galaxy! • Hercules A ~ 1 Mpc ~ 3 million light-years • aka 3C348

With jets coming from the centre

Jets First “real” BH photo

• We seem to see jets • from the Event Horizon Telescope on all scales, from small new stars to giant BH’s • This is how they might work: spinning BH produces wrapped up mag field that focusses particles

Peter Watson Peter Watson April 10, 2019 BH in M 87 Galaxies often come in groups 6.5 billion M0 • 3 galaxies in Draco

Copyright: Giovanni Benintende

Peter Watson Peter Watson

•Which means they can collide •When galaxies •These are the Antennae galaxies collide the stars almost never do, but the clouds of gas do •X-ray picture of the antennae

Peter Watson Peter Watson

•M81 and M82 get very close every 100 million years: •We can see how this might have happened

Credit & Copyright: Leonardo Orazi Peter Watson Peter Watson •M 82 is getting ripped apart •And the “cartwheel” galaxy is a remnant of a much older collision

Peter Watson Peter Watson

•As we look out we see more and more galaxies •Some are tightly packed

•Stefan’s quintet

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•The is made up of 10000 galaxies •But there are more •Apart from one bright star, almost all the objects are galaxies

Peter Watson Peter Watson •And the further out we go, the more we see Quasars

• Bright objects were observed in early radio maps which had no obvious optical counterpart

• Several hundred seen in the 3rd Cambridge catalogue

• In 1960 a faint blue ‘star’ seen at location of 3C48

• Detailed studies made when another blue star found at 3C273

•Quasi-stellar objects…

Peter Watson

Position of 3C273 found v. accurately by lunar This shows the problem: it shows a galaxy (maybe 2) a occultation, so could be identified with 13 mag. blue quasar and a star. Which is which? "star" with jet projecting from it

Except stars don’t have jets!

66 67 Peter Watson Peter Watson

Quasars Radio image of Quasar

• The quasars are much more abundant in the early universe

• They appear to be an early stage of galaxy formation

• As quasars feed on local matter they get heavier

• Most luminous quasars consume 1000 solar masses per year

• Life of the quasar stage is only ~ 106 years

• The resulting massive black holes are clearly related to galaxy formation 76

72 Peter Watson Quasars • The quasars are much more abundant in the early universe • Only object we know that would work is massive hungry black hole • They appear to be an early stage of galaxy formation

• Expect up to 20% of the rest energy of • As quasars feed on local matter they get heavier infalling matter gets converted to some form of radiation • Most luminous quasars consume 1000 solar masses per year

• Life of the quasar stage is only ~ 106 years

74 76 • The resulting massive black holes are clearly related to galaxy formation

Seyfert galaxy: very bright

star-like centre • Quasars very common in early universe.

• Seyfert galaxies seem to be NGC 6814 intermediate between quasars and normal galaxies

• Quasars evolve to Seyferts then to normal spirals as black hole consumes most of central core

HST

Gravitational lensing and quasars Galaxies and “double • About 10000 quasars known quasar”

• Each is very characteristic: red-shifts and spectrum are very distinct.

• However several pairs which lie very close in sky: e.g. 0957 +561A & 0957 +561B are 6" apart in sky and have identical red-shifts. Note "fuzz" sticking out of lower one

HST Can be understood via radio This one is imaged 4 times (the Einstein cross) image: massive galaxies will Can just see the galaxy.

81 82 ESA