March 11, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

March 11, 2003 Lynn Cominsky - Cosmology A350

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Professor Lynn Cominsky

Department of Physics and Astronomy

Offices: Darwin 329A and NASA EPO

(707) 664-2655

Best way to reach me: [email protected]

Astronomy 350Cosmology


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Group 6

Justin Beck Tiffany Henning Pamela Riek Ryan Silva


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Stellar evolution made simple

Stars like the Sun go gentle into that good night

More massive stars rage, rage against the dying of the light

Puff!

Bang!

BANG!


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Exploding Stars

At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!)

Supernova 1987A in

Large Magellanic Cloud

HST/WFPC2


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Supernova Remnants

Radioactive decay of chemical elements created by the supernova explosion

Vela Region

CGRO/Comptel


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Supernovae

Supergiant stars become (Type II) supernovae at the end of nuclear shell burning

Iron core often remains as outer layers are expelled

Neutrinos and heavy elements released

Core continues to collapse

Chandra X-ray image of Eta

Carinae, a potential supernova


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Making a Neutron StarMaking a Neutron Star


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Three views of a Supernova

Lightcurve

SpectrumImage


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Crab nebula

Observed by Chinese astronomers in 1054 AD

Age determined by tracing back exploding filaments

Crab pulsar emits 30 pulses per second at all wavelengths from radio to TeV

movie


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Crab nebula

Radio/VLA Infrared/Keck


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Crab nebula

Optical/HST WFPC2Optical/Palomar


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Crab nebula and pulsar

X-ray/Chandra


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Cas A

~320 years old 10 light years across 50 million degree shell

Radio/VLA X-ray/Chandra

neutron star


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Neutron Stars

Neutron stars are formed from collapsed iron cores All neutron stars that have been measured have

around 1.4 Mo (Chandrasekhar mass)

Neutron stars are supported by pressure from degenerate neutrons, formed from collapsed electrons and protons

A teaspoonful of neutron star would weigh 1 billion tons

Neutron stars with very strong magnetic fields - around 1012-13 Gauss - are usually pulsars due to offset magnetic poles


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Neutron Stars: Dense cindersNeutron Stars: Dense cinders

Mass: ~1.4 solar massesRadius: ~10 kilometersDensity: 1014-15 g/cm3

Magnetic field: 108-14 gauss Spin rate: from 1000Hz to 0.08 Hz


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Distances to Supernovae

Brightest SN in modern times, occurred at t0

Measure angular diameter of ring,

Measure times when top and bottom of ring light up, t2 and t1

Ring radius is given by

R = c(t1-t0 + t2-t0)/2 Distance = R /

Supernova 1987A in LMC

D = 47 kpc


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Distances to Supernovae

Type Ia supernovae are “standard candles” Occur in a binary system in which a white dwarf star

accretes beyond the 1.4 Mo Chandrasekhar limit and collapses and explodes

Decay time of light curve is correlated to absolute luminosity

Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron

Some Type Ia supernovae are in galaxies with Cepheid variables

Good to 20% as a distance measure


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Standard Candles

If you have two light sources that you know are the same brightness

The apparent brightness of the distant source will allow you to calculate its distance, compared to the nearby source

This is because the brightness decreases like 1/(distance)2

movie


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Cosmological parameters

= density of the universe / critical density

hyperbolic geometry

flat or Euclidean

spherical geometry


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Cosmological parameters

In order to find the density of the Universe, you must measure its total amount of matter and energy, including: All the matter we see All the dark matter that we don’t see but we feel All the energy from starlight, background radiation, etc.

The part of the total density/critical density that could be due to matter and/or energy = M

Current measurements : M< 0.3


210 0.2 10.80.60.4

Supernovae & Cosmology

M = matter

= cosmological constant

Redshift


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M = 8 G

3 Ho2

3 Ho2

(total)M +

Einstein meets Hubble

Perlmutter et al.

40 supernovae


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Accelerating Universe

Results from Perlmutter et al. (and also by another group from Harvard, Kirshner et al.) strongly suggest that if = 0.3 :

There is some type of dark energy which is

causing the expansion of the Universe to accelerate

Other results indicate that total = 1 This will be discussed later at much greater length


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Distributions

If sources are located randomly in space, the distribution is called isotropic

If the sources are concentrated in a certain region or along the galactic plane, the distribution is anisotropic


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Classifying Bursts

In this activity, you will be given twenty cards showing different types of bursts

Pay attention to the lightcurves, optical counterparts and other properties of the bursts given on the reverse of the cards

How many different types of bursts are there? Sort the bursts into different classes

Fill out the accompanying worksheet to explain the reasoning behind your classification scheme


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What makes Gamma-ray Bursts?

X-ray Bursts Properties Thermonuclear Flash Model

Soft Gamma Repeaters Properties Magnetar model

Gamma-ray Bursts Properties Models Afterglows Future Mission Studies


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X-ray Bursts

Thermonuclear flashes on Neutron Star surface – hydrogen or helium fusion

Accreting material burns in shells, unstable burning leads to thermonuclear runaway

Bursts repeat every few hours to days Bursts are never seen from black hole

binaries (no surface for unstable nuclear burning) or from (almost all) pulsars (magnetic field quenches thermonuclear runaway)


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X-ray Burst Sources

Locations in Galactic Coordinatesbursters non-bursters Globular Clusters

• Most bursters arelocated in globularclusters or near theGalactic center• They are therefore relatively older systems


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X-ray Burst Source Properties

Weaker magnetic dipole: B~108 GNS spin period seen in bursts ~0.003

sec. Orbital periods : 0.19 - 398 h from X-ray

dips & eclipses and/or optical modulation

> 15 well known bursting systemsLow mass companionsLx = 1036 - 1038 erg/s

Neutron Stars in binary systems


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X-ray EmissionX-ray Emission

X-ray emission from accretion can be modulated by magnetic fields, unstable burning and spin

Modulation due to spin of neutron star can sometimes be seen within the burst


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X-ray Burst Sources

Burst spectra are thermal black-body

Cominsky PhD 1981

L(t) = 4 R2 T(t)4

Radius Expansion

Temperature

2


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Soft Gamma Repeaters

There are four of these objects known to date One is in the LMC, the other 3 are in the Milky

Way

LMC

SGR 1627-41


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Soft Gamma Repeater Properties

Superstrong magnetic dipole: B~1014-15 G NS spin period seen in bursts ~5-10 sec,

shows evidence of rapid spin down No orbital periods – not in binaries! 4 well studied systems + several other

candidate systems Several SGRs are located in or near SNRs Soft gamma ray bursts are from magnetic

reconnection/flaring like giant solar flares Lx = 1042 - 1043 erg/s at peak of bursts

Young Neutron Stars near SNRs


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SGR 1900+14

Strong burst showing ~5 sec pulses

Change in 5 s spin rate leads to measure of magnetic field

Source is a magnetar!


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SGR burst affects Earth

On the night of August 27, 1998 Earth's upper atmosphere was bathed briefly by an invisible burst of gamma- and X-ray radiation. This pulse - the most powerful to strike Earth from beyond the solar system ever detected - had a significant effect on Earth's upper atmosphere, report Stanford researchers. It is the first time that a significant change in Earth's environment has been traced to energy from a distant star. (from the NASA press release)


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Gamma Ray Burst Properties

Unknown magnetic field No repeatable periods seen in bursts No orbital periods seen – not in binaries Thousands of bursts seen to date – no

repetitions from same location Isotropic distribution Afterglows have detectable redshifts which

indicate GRBs are at cosmological distances (i.e., far outside our galaxy)

L = 1052 - 1053 erg/s at peak of bursts

A cataclysmic event of unknown origin


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The first Gamma-ray Burst

Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery!

Vela satellite


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Compton Gamma Ray Compton Gamma Ray ObservatoryObservatory

• Eight instruments on corners of spacecraft• NaI scintillators

BATSE


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CGRO/BATSE Gamma-ray Burst Sky

Once a day, somewhere in the Universe


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The GRB GalleryThe GRB Gallery

When you’ve seen one gamma-ray burst, you’ve seen….one gamma-ray burst!!


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Near or Far?Near or Far?

Isotropic distribution implications:

Silly or not, the only way to be sure was to findthe afterglow.

Very close: within a few parsecs of the Sun

Very far: huge, cosmological distances

Sort of close: out in the halo of the Milky Way

Why no faint bursts?

What could produce such a vast amount of energy?

A comet hitting a neutron star fits the bill


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Breakthrough!Breakthrough!In 1997, BeppoSAX detects X-rays from a GRB

afterglow for the first time, 8 hours after burst


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The View From Hubble/STIS The View From Hubble/STIS

7 months 7 months laterlater


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On a clear night, you really On a clear night, you really cancan see forever!see forever!

990123 reached 9th magnitude for a few moments!

First optical GRB afterglow detected simultaneously


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The Supernova ConnectionThe Supernova Connection

GRB011121Afterglow faded like supernova

Data showed presence of gas like a stellar wind

Indicates some sort of supernova and not a NS/NS merger


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Hypernova

A billion trillion times the power from the Sun The end of the life of a star that had 100 times the mass of our Sun

movie


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Iron lines in GRB 991216

Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB 991216

Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions


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Catastrophic Mergers

Death spiral of 2 neutron stars or black holes


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Which model is right?Which model is right?

The data seem to indicate two kinds of GRBs

• Those with burst durations less than 2 seconds• Those with burst durations more than 2 seconds

Short bursts have no detectable afterglows so far as predicted by the NS/NS merger model

Long bursts are sometimes associated with supernovae, and all the afterglows seen so faras predicted by the hypernova merger model


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Gamma-ray Bursts

Either way you look at it – hypernova or merger model

GRBs signal the birth of a black hole!


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Gamma-ray Bursts

Or maybe the death of life on Earth?

No, gamma-ray bursts did not kill the dinosaurs!


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How to study Gamma rays?

Absorbed by the Earth’s atmosphere

Use rockets, balloons or satellites

Can’t image or focus gamma rays

Special detectors: crystals, silicon-strips

GLAST balloon

test


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HETE-2

Launched on 10/9/2000Operational and finding about 2 bursts

per month


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Swift Mission

Burst Alert Telescope (BAT)

Ultraviolet/Optical Telescope (UVOT)

X-ray Telescope (XRT)

To be launched in 2003


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Swift Mission

Will study GRBs with “swift” response Survey of “hard” X-ray sky To be launched in 2003 Nominal 3-year lifetime Will see ~150 GRBs per year


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Gamma-ray Large Area Space Telescope

GLAST Burst Monitor (GBM)

Large Area Telescope (LAT)


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GLAST Mission

First space-based collaboration between astrophysics and particle physics communities

Launch expected in 2006Expected duration 5-10 yearsOver 3000 gamma-ray sources will be seen


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GRBs and Cosmology

GRBs can be used as standard candles, similar to Type 1a supernovae

However, the supernovae are only seen out to z=0.7 (and one at z=1.7), whereas GRBs are seen to z=4.5, and may someday be seen to z=10

Schaefer (2002) has constructed a Hubble diagram for GRBs, using the cosmological parameters from supernova data. When more burst redshifts become available (e.g., from Swift), the parameters can be determined independently


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The Great Interplanetary GRB Hunt

Using data from several satellites in the solar system, you will use a “light ruler” to figure out the direction to a gamma-ray burst

This is similar to the way that the Interplanetary Network (IPN) really works

See http://ssl.berkeley.edu/ipn3/


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Web Resources :

GLAST E/PO web site http://glast.sonoma.edu Swift E/PO web site http://swift.sonoma.edu Imagine the Universe! http://imagine.gsfc.nasa.gov Science at NASA’s Marshall Space Flight Center http://science.nasa.gov Supernova Cosmology Project http://panisse.lbl.gov/ Ned Wright’s ABCs of Distance http://www.astro.ucla.edu/~wright/distance.htm


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Web Resources

Robert Duncan’s magnetar page http://solomon.as.utexas.edu/~duncan/magnetar.html Chandra observatory http://chandra.harvard.edu

Jochen Greiner’s Gamma-ray bursts and SGR Summaries http://www.mpe.mpg.de/~jcg

HETE-2 mission http://space.mit.edu/HETE/

Compton Gamma Ray Observatory http://cossc.gsfc.nasa.gov/

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March 11, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

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