Download What is X-ray Astronomy? - Extreme Universe Laboratory

Introduction and Overview
1. X-ray/Gamma-ray Astronomy.
2. The Great Observatories.
3. Chandra.
4. High Energy Astrophysics
5. Sample Sources
Professor George F. Smoot
Extreme Universe Lab, SINP
Moscow State University
Great Observatories
Opacity of Atmosphere
Versus characteristic temperature
characteristic temperature
characteristic temperature
Chandra
X-ray Producing Collision
Synchrotron Radiation
Inverse Compton Scattering
Atomic Emission
Birth of an X-ray
Chandra:
Revolution through Resolution
Martin Elvis, Chandra X-ray Center
The Chandra X-ray Observatory
Launched 23 July 1999
revolutionized X-ray astronomy,
and all of astronomy.
What is X-ray Astronomy?
What is Chandra?
Why has Chandra done its job so well?
And what exactly has Chandra done?
What is X-ray Astronomy?
When we look up at the night sky
we see it filled with stars
Outside the narrow range of colors
our eyes are sensitive to,
something quite different dominates
the night sky…
Powerful sources of X-rays
X-ray map of the whole sky:
Rosat All Sky Survey (MPE)
100,000 `sources’
A power source entirely different from the nuclear fusion that drives the Sun and stars
…and much more efficient
X-ray Astronomy tries to find out what could cause such extraordinary power
X-ray Astronomy studies short wavelength light from the Universe
Whipple 10 meter
1015 range of wavelength in astronomy
million billion between shortest & longest
X-rays
1/1000
Compton gamma-ray
Observatory
Chandra
Visible
Hubble
MMT
1/1000
Sub-millimeter array
VLA
Compare Visible light and X-rays:
“1000 times”
X-rays have:
 Wavelengths: 1/1000 visible light
 0.1-6 nm (1-60A) vs. 500 nm (5000A)
 Energies: 1000 x visible light
 “keV” instead of “eV” (electron volts)
 About 0.02 Joules/photon
 Temperatures: 1000 times hotter
 10 million degrees vs. 10 thousand degrees
for stars
 E=kT
(k= Boltzman’s constant, 1.398x10-9 J/K)
SNR G292.0+1.8 (Hughes et al.)
What gets so hot?
• Surely not much can get so hot as a million degrees?
• Oh yes it can…
Explosions: Supernovae and
their remnants
Particles moving near the
speed of light in magnetic
fields
Supernova 1987a
Crab Nebula
Matter falling into deep
gravitational wells
Abell 2029
Cluster of galaxies
¼ sun – a centauri
sun
a centauri
sun
Andromeda
nearest galaxy
Sounds obscure but …
gravity power is the most common source of X-rays in the sky
40 Years of X-ray Astronomy:
1 billion times more sensitive
1962
Sco X-1: the brightest source of Xrays in the sky
Good for 1 (one) Nobel Prize
2001
Chandra
1978
good enough
for my thesis
Distant galaxy 100,000 times
fainter than NGC3783
Moon to scale
NGC3783: a quasar appearing
10,000 times fainter than Sco X-1
1999
Resolution is the key
Chandra takes X-ray Astronomy from its
‘Galileo’ era to its ‘Hubble’ era in a single leap
Sharpest Detail detectable
0.1”
1”
Galileo
10”
100”
Hubble Space
Telescope
Chandra
Dawn of History
1600
1700
1800
1900
2000
Year
X-ray astronomy took just 40 years to match 400 years of optical astronomy
What is Chandra?
Chandra is the greatest X-ray Observatory ever built
Orbits the Earth to be above the atmosphere (which absorbs X-rays, luckily!)
Goes 1/3 of the way to the Moon
every 64 hours (22/3 days)
Chandra takes superbly sharp images:
‘high resolution imaging’
X-ray Telescopes are different
Chandra’s mirrors are almost cylinders
X-rays don’t reflect off a normal mirror – they get absorbed.
Only by striking a mirror at a glancing angle, about 1o,
do X-rays reflect.
Then they act like visible light
and can be focused
This makes for looooooooong telescopes
Chandra is as big as a moving truck
10 meters (32 ft) from mirror to detector, 1.2 meters (4ft) across mirror
…but focuses X-rays onto a spot only 0.025mm (1/1000 inch) across
That’s why Chandra is powerful
Chandra detects individual photons
Uses Wave-Particle Duality of Light
CCD
detectors
count each
X-ray
individually
each X-ray knocks free
enough electrons to
detect as a pulse of
electricity
Light as particles
…but can disperse the incoming X-ray light: Light as Waves
Delicate gold gratings diffract the light
Chandra provides a great example
of how
Quantum wave/particle duality
works in a real machine
Chandra’s sharp focus revolutionizes our
understanding
SPACE IMAGING
Earth observing satellite equivalents of …
Best X-ray image of
whole sky (ROSAT)
Any sign of life?
Best X-ray images before
Chandra (ROSAT)
What’s this odd
thing?
Chandra images
I get it!
Like looking up the answers at the back
of the book
Chandra has solved 20 year old
mysteries in just one shot:
Yes – the background X-ray light is made up of
contributions from millions of quasars
No – gas is not pouring down onto the galaxy
at the center of a cluster of galaxies.
Something stops it, but what?
Yes -- Our Milky Way sits in a bath of hot gas
stretching to the Andromeda galaxy and
beyond
Yes – quasars have hot winds blowing from
their cores, at 2 million miles per hour
…but also being given a whole new SAT
test, without taking the class
2 examples: What are we looking at?
Antennae – colliding galaxies
Centaurus A – nearest quasar
X-ray ‘smoke ring’ from explosion in core?
Nest of super-bright black holes in
binaries – bigger than any star?
Chandra’s Revolution through Resolution
continues…
Chandra set to run for 5
more years
& may last much longer
Deeper looks show
•more and more detail,
•more and more surprises
Antennae: Deep Exposure
High Energy Astrophysics
• High energy astrophysics typically deals with x-rays and
higher energy radiation. It also deals with high energy
neutrinos and other particles such as protons, electrons,
positrons etc.
• High energy radiation is produced by objects at high
temperatures and/or relativistic particles.
1 ev = 10,000 K,
1 kev = 107 K
• This usually requires compact objects such as white dwarfs,
neutron stars or blackholes with deep gravitational potential.
Vesc=(2GM/R)1/2 approaching c
Or R not much greater than the Schwarzschild radius:
2 GM/c2 (2.95 km for a solar mass object).
Roentgen
historic
X-ray
X-ray astronomy: 0.1 to 100 kev
Gamma-ray astronomy: >100 kev.
E=hn= k T ==> x-rays probe 106 -- 109 K
and gamma-rays > 109 K
Eddington Luminosity: 1.3x1038 erg/s for 1 Mo.
(derive the Eddington limit)
Optically thick blackbody radiation in x-ray requires a compact object!
T as a function of object mass, radius (in units of Schwarzschild radius)
and Luminosity (in units of Eddington luminosity), is given by:
T ~ 7 kev (L/L_Edd)^{1/4} (R/R_s)^{-1/2} (M/M_sun)^{-1/4}
Thus if the radiation is black-body and luminosity is close to Eddington,
Then x-ray temperature is reached provided that R\sim R_s and
M is not much greater than M_sun.
This result is violated, as it often is, when the radiation is non-thermal.
Brief Property and History of Compact Objects
1. 1914: Adams-- Sirius B has M~ 1Mo, T~ 8000 K, R~10,000km
2. 1925: Adams confirmed M & R by measuring gravitational
redshift -- z ~ GM/(R c2)=0.0003.
3. 1926: F-D statistics discovered. Fowler applied it to model WDs.
4. 1930: Chandrasekhar: WD model including relativity; mass limit.
5. 1983: Nobel prize to Chandrasekhar.
White dwarfs:
R~10,000 km, Vesc~0.02 c, density~ 106 g/cc
(Nuclear reaction is more efficient source of energy
than the PE release of in-falling gas on WDs).
Neutron Stars
1. 1931: Chadwick --discovers neutrons.
2. 1934:Baade & Zwicky suggested neutron-stars, and
postulated their formation in supernovae.
3. 1967: Hewish, Bell et al. Discover radio pulsars.
4. 1968: Gold proposed rotating NS model.
5. 1974: Nobel prize to Ryle (aperture synthesis) Hewish (pulsars).
6. 1975: Hulse & Taylor discover binary pulsar PSR 1913-16.
7. 1993: Nobel prize to Hulse & Taylor.
Neutron stars:
R~15 km, Vesc~0.32 c, density~ 1014 g/cc
(Nuclear reaction is much less efficient source of energy
than the PE release of in-falling gas on NSs - gravitation).
Black Holes
1795: Laplace noted the possibility of light not being able to escape.
1915: Einstein’s theory of general relativity.
1916: Schwarzschild -- metric for a spherical object
1963: Kerr --metric for a spinning BH.
1972: Discovery of Cyg X-1
1995: Miyoshi et al. -- NGC 4258.
1997: Eckart & Genzel -- (Sgr A*) Galactic center.
Schwarzschild radius = 2.95 km M/Mo
Efficiency of energy production 6% to 42%.
2002: Nobel prize in physics to Giacconi (x-ray astronomy).
Summary
1. Derivation of the Eddington limit.
2. We
found that bright sources of high energy
photons are typically compact objects such
as WD, NS or BH.
High speed, strong, shocks are another way
of generating high energy photons; however
high speed shocks are usually produced when
compact objects form eg. SNe, GRB etc.
(an exception is x-rays from clusters.)
Atmospheric Transmission
(1 Ao = 12.5 kev)
Eary All Skly Catalog
EUV picture of the Sun at 171 A = 74 ev (SOHO)
Coronal luminosity:
~ 1026 erg/s
EUV picture of the Sun at 171 A = 74 ev (SOHO)
Corona &
several
Active
regions
are visible
EUV picture
of the Sun at
195 A = 65 ev
from
SOHO
Corona, active regions
and a flare are visible
Sun approaching Solar Max
at 195 A = 65 ev
Accretion to create X-ray binary
An artist’s view
Crab Pulsar
Blue: x-ray
Red: optica
Green:radio
Luminosity ~ 1038 erg/s
(mostly x-ray & gamma)
Synchrotron radiation:
(linear polarization of 9%
averaged over nebula).
Electrons with energy > 1014 ev
are needed for emission at 10 kev;
lifetime for these e’s < 1 year.
So electrons must be injected
continuously & not come from SNe.
Crab nebula
(Plerion)
Crab redux
Plerion: is derived from the Greek word “pleres” which means “full”.
Crab nebula is the remnant of Sne explosion (perhaps type II) observed by the Chinese
Astronomers in 1054 (July 4th). The pulsar at the center has a period of 33milli-sec.
Crab shows pulsed emission from radio to optical to >50 Mev!
Moreover, The pulse shape is nearly the same over this entire EM spectrum,
suggesting
A common origin for the radition which is believed to be synchrotron
(curvature radiation). The radio is produced not too far away from the
Neutron star (within 5-10 radii) and high energy pulsed radiation is
Likely produced near the light cylinder.
The bolometric luminosity is pulsed radiation is about a factor 100 smaller
Than nebular radiation; pulsed radio is smaller than total pulsed radiation
By a factor of 10^4.
SN remnant: Cas A (3-70 kev; Chandra) Plerion
SNe II remnant
Age 300 yr
(1670 AD)
X-ray luminosity:
3.8x1036 erg/s
Mass of x-ray gas
10-15 solar mass.
Pulsar wind nebula G292(Chandra 3-80 kev) (Plerion)
SN remnant G11.2-0.3 in x-ray (Chandra)
X-ray luminosity:
~ 1036 erg/s.
The radiation is
produced by shock
heated gas at ~ 109 K
via bremsstrahlung.
Note the bright (blue)
Pulsar nebula at the
Center.
Produced in SN of 386 AD
Gamma-ray burst: note the relativistic jet, and supernova explosion
AGN jet from the quasar GB 1508+5714 (distance 4Gpc)
Chandra x-ray obs.
Obs. jet size~30 kpc
(x-ray produced
by IC of CMB-photons
with jet e-s)
Centaurus A
(distance ~ 2.5 Mpc)
HST & 6 cm VLA
VLA: 6 cm
Radio lobe size ~ 200 kpc!
The radio lobes are fed by
relativistic jets; we see only
one sided jet due to
relativistic beaming.
NGC 4261
Stephan’s Quintet
Blue:
Chandra x-ray
Yellow:
SDSS optical
Compact group of interacting
galaxies. Gas is stipped and
shock heated to 6 million K
produces x-rays.
F is a foreground galaxy. So the
cluster (A, B, D & E) is in fact
a quartet.
Cluster X-ray & Optical
Chandra x-ray; ~ 2 kev
Abel -2390
0.5 Gpc
MS2137.3-2353
(1 Gpc)
HST - optical image
(note lensing of background gals)
SN remnant G11.2-0.3
M87 jet