Introduction to Astrophysics - RHIGrhig.physics.wayne.edu/reu/new_talks/introastro2013.pdf · Introduction to Astrophysics Professor David Cinabro 1 Thursday, April 25, 2013. Disclaimer

Introduction to Astrophysics

Professor David Cinabro

1

Thursday, April 25, 2013

Disclaimer

• Subject is vast• Covers everything from Physics of the

Atmosphere to the Origin and Fate of the Universe and everything in between

• Impossible to introduce all of it in ~1 hour

• Focus on research we do here– Professor Cinabro - Cosmology with SN– Professor Hackett - Accretion 2


Cosmology with Supernovas

David Cinabro


Cosmology Background• The study of the origin and evolution of

the Universe.• Last 20 years have been a “golden age”

in which we have learned:– Origin is a giant explosion known as the

Big Bang– Fate is most likely continued expansion– Most of the Universe is in the Dark Sector:

• Dark Matter: Unknown sort that dominates over ordinary matter

• Dark Energy: Unknown force that is pushing the Universe apart


Discovery of the Expanding Universe: Hubble 1929

Finds that thevelocity gets larger with distance, the Hubble Law, and slope is the Hubble parameter, H

Measured distances to 25 galaxies:• Used cepheids for Andromeda and Local Group• Used brightest stars in the others• Compared distances with recession velocities.


Echo of the Explosion: Gamow (1948)• Gamow and Alpher consider

the consequences of an expanding Universe.

• First conclusion is that the Universe should be filled with E+M radiaHon leI over from when it was small and hot.

• Today should be Microwaves (Blackbody with T = 3K).


Cosmic Microwaves (1963)• Serendipitously observed at Bell Labs using a communicaHons instrument.

• Death blow to alternate Steady State cosmology of Fred Hoyle.


Astronomer’s Periodic Table• Gamow, Alpher, Herman add in Nuclear Physics to calculate the abundances of the elements arising from the hot, dense early Universe (1948-‐56).

• Agrees with observaHons that grow increasingly precise.


Triumph of the Big Bang• Ironically the term was coined ironically by Fred Hoyle, supporter of Steady State, in a 1949 radio broadcast.

• Three pillars:

1) Expanding Universe

2) Cosmic Microwave Background

3) Cosmic Elemental Abundances

• Only serious Cosmology by the mid-‐1970’s

• Unfortunately it leaves only two alternaHves for the fate of the Universe…


Big Bang starts the expansion of the universe. But there is enough mass in the universe that gravity captures all the galaxies, the universe begins to contract, making gravity stronger, accelerates contracHon, and eventually the universe is compressed into a single point(?). We call this…


The Big Crunch

Big Bang starts the expansion of the universe. But there is enough mass in the universe that gravity captures all the galaxies, the universe begins to contract, making gravity stronger, accelerates contracHon, and eventually the universe is compressed into a single point(?). We call this…


Big Bang starts the expansion of the universe. But there is not enough mass in the universe for gravity to capture the galaxies, and the universe expands, at an ever slowing rate, forever. Stars begin to run out of fuel and burn out, and since the universe gets less and less dense no new stars form. It gets colder and colder unHl the universe freezes to death. We call this…


The Big Chill

Big Bang starts the expansion of the universe. But there is not enough mass in the universe for gravity to capture the galaxies, and the universe expands, at an ever slowing rate, forever. Stars begin to run out of fuel and burn out, and since the universe gets less and less dense no new stars form. It gets colder and colder unHl the universe


Cosmic Microwave BackgroundSnap shot of matter density of the universe at the photon surface of last scattering. Most accurate from Planck satellite.


M51: June 2005 M51: July 2005


Galaxy Clustering(Daniel Eisenstein)








Galaxy ClusteringObserve this in the distance between neighboring galaxies in large galaxy surveys such as Sloan Digital Sky Survey


Describing the Universe

• How Astronomers describe the Universe on the cosmological scale.

• Repulsive cosmological constant(Λ) versus agracHve mass(m).

• 1.0 = Enough agracHve to force Big Crunch.

Ω

Ω

Λ

m1.0

1.0

Big Chill

Big Crunch

No Big Bang

0.0


Concordance Model Cosmology

• Another three pillars

1) CMB map

2) SNIa vs redshiI

3) Galaxy clustering

• Dark Energy is most like a strong version of Einstein’s Cosmological Constant


Cosmologies Golden Age

• The Universe is mostly stuff about which we are IGNORANT.

• Countless explanaHons, but none are very saHsfying and as yet no experiment or observaHon are decisive on the nature of the Dark Sector.


Sloan Digital Sky Survey Supernova Search

• World’s sample of Supernovas is quite small (~1000)

• More would allow tests of Dark Energy (Is it constant in time? Is it constant in

space?)• Sloan Digital Sky Survey ideal for this

work (www.sdss.org)


Supernova Candidate


Asteroid




Core Collapse SN Rate

29


Galaxy Host Properties

30


Galaxy Host Properties

31


CCD R&D at LBNL

32


REU Student Opportunities

• Vast• Continued analysis of SDSS-SN data set:

Comparison of model CCSN with real CCSN, Hostless SN... Opportunities at FNAL.

• MS-DESI: Take astro spectra like SDSS took images. CCD R&D work at LBNL.

• LSST: Monster scale up of SDSS. Workers needed for simulation and hardware. Opportunities at SLAC.

• Development of SN Software Analysis package SNANA. Work with WSU Comp Sci. 33


ACCRETION POWER IN ASTROPHYSICS

Professor Cackettac・cre・ tion \a-ʻkrē-shən\: noun

the process of growth or enlargement typically by the gradual accumulation of additional layers or matter


ACCRETION

• Accretion: process by which an object gains/accumulates mass

• Extremely important process throughout the Universe from young stars to supermassive black holes at the centers of galaxies

A young star forming and accreting matter from a disk

Credit: Hubble Space Telescope

Disk of gas

Jet

Artist’s impression of accretion onto a black hole


A SOURCE OF ENERGY• Extraction of gravitational

potential energy as material accretes onto a massive object

➡ gravitational potential energy converted to radiation through friction

• Due to conservation of angular momentum, accreting material usually forms a rotating thin disk

Accretion in binary system

Accretion disk


MORE EFFICIENT THAN FUSION!• Nuclear fusion, which powers

stars, is less than 1% efficient for H ➞ He:

Enuc = 0.007 mc2

• Energy from accretion is given by:

Eacc = GMm/R

• For compact objects (neutron star or black hole) accretion is greater than 20 times more efficient than fusion!

Nuclear fusion powers stars like the Sun


MAXIMUM ACCRETION RATE

• As Eacc = GMm/R the more massive an object and the smaller it is, the greater the energy released through accretion

• But, there is a limit to how much energy is radiated away, the Eddington Limit: inward gravitational force on matter must be greater than the outward radiation pressure otherwise it would blow itself apart

Einstein & Eddington at the University of Cambridge


COMPACT OBJECTS

• Accretion most powerful onto compact objects

• Black hole: a massive object whose gravitational force is so strong that not even light can escape

• Neutron star: a star about 1.5 times the mass of the Sun, but with a radius of only ~10 km - a star the size of a city!

Light near a black hole gets bent by the strong gravity there


BLACK HOLESCome in several ‘flavors’:

• stellar-mass black holes (~10 Msun)

➡ formed in supernovae

• supermassive black holes (106 - 109 Msun)

➡ found at the centers of galaxies

Stars orbiting around the black hole at the center of the Milky

Way


BLACK HOLESCome in several ‘flavors’:

• stellar-mass black holes (~10 Msun)

➡ formed in supernovae

• supermassive black holes (106 - 109 Msun)

➡ found at the centers of galaxies

Stars orbiting around the black hole at the center of the Milky

Way


QUASARS• aka ‘Active Galactic Nuclei’

• Light from the central region outshines the entire galaxy!

• Only way to power is by accretion of gas onto a black hole

• Using the ‘Eddington Limit’ can estimate that black holes at the centers of galaxies must be typically between 106 - 109 Msun

The M87 Jet

PRC00-20 • Space Telescope Science Institute • NASA and The Hubble Heritage Team (STScI/AURA)

A nearby Active Galactic Nucleus shoots a high-

speed jet of gas

Light from accretion disk


STELLAR-MASS BLACK HOLES

• Can be formed in a supernova explosion at the end of a massive star’s life

• Often found in binary systems

• Black hole can accrete matter from the companion star!

Matter can be pulled from the companion star to the black hole


NEUTRON STARS• Also can be formed in

supernovae

• About 1.5 Msun in 10 km radius

• average density > than atomic nuclei

• densest observable matter in Universe

• made mostly of neutrons, but may contain exotic matter at the center

Inne

r C

ore: ?

Out

erCore

: n, p

, e

Crus

t: nucle

i, n, e

Where ? could be: hyperon condensate, kaon condensate,

strange quark matter...........


NEUTRON STARS

• Like stellar-mass black holes, can often be found in binary systems

• Can also accrete matter from the companion star

Accretion onto a neutron star


OBSERVING ACCRETION ONTO COMPACT OBJECTS

• Gas accreting onto black holes and neutron stars gets extremely hot (millions of degrees)

• The gas therefore emits thermally in X-rays

An all-sky X-ray image: the brightest X-ray sources in the sky come from accretion onto black holes and neutron stars

From MAXI onboard the ISS


X-RAY TELESCOPES• X-rays do not penetrate the

Earth’s atmosphere, so have to go into space

• X-rays will pass through conventional optical telescope mirrors, so have to focus X-rays with special ‘grazing-incidence’ mirrors

• Major NASA and ESA missions are : Chandra and XMM-Newton

CHANDRA

XMM-NEWTON


OBSERVING X-RAYSTHE

CHANDRA MIRRORS


ACCRETION SUMMARY

• Accretion onto compacts objects is the ultimate power source in the Universe

• Prof. Cackett works on X-ray observations of accretion onto black holes and neutron stars to try and understand these objects

• Renee Ludlam will be working with Prof. Cackett this summer.


Astrophysics Summary• Plenty of work to do. Last 2 years 6 projects.• Zaven Bush (galaxy vs. CCSN)• Johanna-Laina Fischer (new parameters in

SNIa light curves), Levente Dojcsak(new fitting model to SNIa light curves-led to a paper) at FNAL with John Marriner.

• Brett Sandler to SLAC worked with Rafe Schindler on IR Camera for DES.

• Rachael Merritt SN Host vs Field Galaxies, Aron Zell accretion in NS, Meridith Joyce on resolution of DES camera


Documents

Introduction to Astrophysics - RHIGrhig.physics.wayne.edu/reu/new_talks/introastro2013.pdf · Introduction to Astrophysics Professor David Cinabro 1 Thursday, April 25, 2013. Disclaimer