ASTR 2020
Space Astronomy
Week 8:
Massive stars, binaries
high-energy processes
Black holes, Dark matter, Dark energy
Announcements:
- Midterm #1 date change:
Friday 14 to Monday 14 March
- HW#4 due this Friday (5 Mar).
Most massive stars are
In multiple systems!
Multiplicity is rare
Among low-mass stars
Close
Binary Star
Evolution:
Roche
Lobe
Overflow
100 meter diameter Green Bank Telescope (GBT)
in West Virginia
Globular cluster M22
old neutron stars
in binary,
- spun-up by
accretion from dying
red-giant star
W50
SNR (VLA)
Supernova 1987a in the LMC:
Superkamiokande
(Japan)
Neutrino detector
Superkamiokande (Japan) Neutrino detector
Neutrino flash from Supernova 1987a
TeV photons, Cosmic Rays
Air-Cherekov radiation
H.E.S.S. array (Namibia)
HESS J1632-478: an energetic relic in the Galactic plane
(Balbo 2010): Pulsar (neutron star) + pulsar wind nebula
-ray
infrared
UV
radio
visual
X-ray
-ray
(H.E.S.S.)
Supernova SN 185 AD
X-ray (~keV / photon)
HESS TeV (~1012 erg / photon )
Two relativities:
Special relativity: How time and space behave
- Does not include gravity (no accelerations)
- Differs from Newton at velocities close to c.
- Nothing can move faster than c (locally)!
- Mass is a form of energy (E = mc2)
- Space and time intimately connected
General relativity: More complete picture of space-time & gravity
- Include gravity & accelerations
- Mass/energy tells space-time how to curve
- Curved space-time tells matter & energy how to move
- Fundamental for understanding cosmology
ASTR 2020
Space Astronomy
Week 8:
Massive stars, binaries
high-energy processes
Black holes, Dark matter, Dark energy
Announcements:
- Midterm #1 date change:
Friday 14 to Monday 14 March
- HW#4 due this Friday (5 Mar).
Black Holes
Gravitational Escape Speed = Speed of Light
(300,000 km/second)
Observed:
Massive stars => Supernovae =>
Stellar mass Black Holes
Galactic Nuclei => quasars, radio galaxies
Super-massive Black Holes
Speculated:
Big-Bang =>
Mini Black Holes ?
Universe => ‘time-reversed’ Black Hole ?
Black holes:
Escape speed = speed of light
R = 2 GM / c2 ~ 3 km/s x Mass(Solar masses)
Stellar mass black holes: M = 1 to 100 Mo
Remnants of core collapse supernovae
of stars with initial mass M > 30 Solar masses
Intermediate-mass black holes:
Centers of Globular clusters ?
Super-massive black holes:
In centers of Galaxies: 106 - 1010 Mo
Mini black holes?
Formed in Big Bang?
Minimum mass due to Hawking radiation
Stellar-mass Black Holes
Escape Speed = speed of light
Become visible indirectly as matter spirals into
them
Stellar-mass black holes:
Massive stars
=> core collapse supernovae (Type II)
Core mass < ~ 5 Mo =>neutron star
Core mass > ~ 5 Mo => black hole
hole
- Long duration gamma-ray bursts
jets form during core collapse to black
- Time variable X-ray sources
Continued accretion onto black hole
from binary companion
gamma-ray bursts
jets form during core collapse of massive star to black hole
Galaxy Clusters
reveal dark matter
Galaxy velocities too large
to be explained by gravity
of visible galaxies
Velocity dispersion:
random motion along
line-of-sight (Doppler)
Expected ~ 100 km/sec
found ~ 1000 km/sec!
1930’s by Fritz Zwicky
Spiral galaxy
ROTATION
CURVES
 Discovered by Vera Rubin in
the 1970’s
Galaxy Rotation Curves are FLAT !!!
…but light (ordinary matter) decreases with R
=> dark matter !
Use Doppler shift to measure motions at different radii
Remember:
V2 = GM / R
Mass INSIDE the orbit radius, R
M(<R) = RV2 / G
If (r) ~ R-2
M (<R) => R3 R-2 => R
V2 = constant !
V = constant => “flat rotation curve”
But, light Flux(R) decreases exponentially => M / L INCREASES with R !!
M82 – Subaru 8-m (Mauna Kea)
Absorption (dust,
the “D” lines of Na I,
The “H” and “K” line of Ca, …)
Emission line
6562 A Ha
6548, 6584 A [NII]
Slit of Spectrograph
continuum
emission (stars
Spectrum of M82 along major axis:
“rotation curve” (from Doppler shift)
[S II
[NII] Ha [NII]
Flat rotation curves
Note that the bright parts of the galaxy are about
30,000 ly across
Vrotation = (GM/R)1/2
Mass INSIDE R is increasing, (M/R ~ constant !!!)
yes amount of light (traces stars) is decreasing !!!
The average M/L for a galaxy RISES farther out
M/L ~ 10-20
(and as high as 50 for a few) at the largest radii
M/L too big for normal stars…
ASTR 2020
Space Astronomy
Week 8:
Dark matter, Dark energy
Announcements:
- Midterm #1 date change:
Friday 14 to Monday 14 March
- HW#4 due this Friday (5 Mar).
Galaxy Clusters
reveal dark matter
Galaxy velocities too large
to be explained by gravity
of visible galaxies
Velocity dispersion:
random motion along
line-of-sight (Doppler)
Expected ~ 100 km/sec
found ~ 1000 km/sec!
1930’s by Fritz Zwicky
The average M/L for a galaxy RISES farther out
M/L ~ 10-20
(and as high as 50 for a few) at the largest radii
M/L too big for normal stars…
Dark Matter
•
Ordinary matter (stars, gas, dust) traced by light
(X-rays, UV, light, IR, radio)
Evidence for Dark Matter (its gravity!)
1.
2.
3.
Speed of galaxies in clusters is too large
Not enough ordinary matter to explain motions
The orbits of stars & gas in galaxies
Speeds remain high in outer parts beyond stars & gas
Gravitational lensing
Gravity traces ALL types of matter, energy
=> gravity implies 5 X more matter than we see!
=> It’s dark - does NOT interact with light or
nuclear forces.
Gravitational Lens
Gravitational Lens
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Gravitational Lens
Background galaxy
foreground cluster
Dark Matter: What is it?
•
MAssive Compact Halo Objects (MACHOs)?
black holes, neutron, stars, other forms of
ordinary matter in collapsed form
- Probably not !
•
Weakly Interacting Massive sub-atomic Particles
(WIMPs)
Interact only with gravity, weak nuclear forces!
(NOT with electro-magnetism or strong force)
=> “super-symmetric” partners to
neutrino, photon, electron, …. ?
(neutralino, photino, selectron, ….)
WIMPs
The Expanding Universe
Velocity = H0 x Distance
H0 ~ 72 km s-1 / Mpc
(km / mega parsecs)