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Mar 24, 2024 249 likes •641 views

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies ID IDTERM # #2 : ID IDTERM # #2 EXT ursday 10/15: EXT Tuesday 10/20: earching for dist earching for dist

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SLIDE 1

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies

EXT Tuesday 10/20:

earching for dist

stant world earching for dist stant world

GO DIRECTLY TO THE PLANETARIUM

EXT ursday 10/15: : ID

IDTERM # #2 ID IDTERM # #2

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SLIDE 2

The Stellar Graveyard The Stellar Graveyard

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SLIDE 3

What What’ ’s In The Stellar Graveyard? s In The Stellar Graveyard?

  • Lower mass stars white dwarfs

– Gravity vs. electron degeneracy pressure

  • High mass stars neutron stars

– Gravity vs. neutron degeneracy pressure

  • Even more massive stars

Even more massive stars (M>30-40 (M>30-40 M Msun

sun)

) black black holes holes

– Gravity wins

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SLIDE 4

When the mass is too great When the mass is too great for even neutron for even neutron degeneracy degeneracy to hold up to hold up… …

  • Our supernova core

collapses to an infinitely small point Black Hole

Black Hole

when Mcore > 3 Msun

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SLIDE 5

Black Holes Black Holes – – sort of

sort of

courtesy of Albert

courtesy of Albert

  • Einstein

Einstein’ ’s (1911) s (1911) General Theory of General Theory of Relativity Relativity: : gravity is gravity is really the really the warping of warping of spacetime spacetime around an around an

  • bject with much mass
  • bject with much mass
  • Light travels in

Light travels in “ “straight straight lines lines” ” – – and its and its bending bending comes from comes from spacetime spacetime being curved by gravity being curved by gravity

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SLIDE 6

GENERAL RELATIVITY: (in a nutshell) asses pacem how curve. pacem, i it urvature, , s masse how move.

[Image from “Spacetime and Gravity” by S. Carroll]

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SLIDE 7

[Image by R. Jantzen]

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SLIDE 8

Effects of strong Effects of strong gravity on light gravity on light

can act like lens can act like lens can can redshift redshift light light

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SLIDE 9

Two images of a distant quasar

A B

[Image credit: R. Ellis & I. Smail with HST (NASA/STScI)]

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SLIDE 10

Source behind the lens: EINSTEIN RING

[Image credit: L. King with HST (NASA/STScI)]

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SLIDE 11

The arches are the result of gravitational lensing

[Image credit:

  • P. Natarajan with HST

(NASA/STScI)]

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SLIDE 12

What is the theory of General What is the theory of General Relativity? Relativity?

  • A. A theory that describes gravity in terms of

forces between massive bodies

  • B. A theory that describes gravity in terms of

spacetime curvature

  • C. The most general theory of the Universe
  • D. A theory that describes the atom
  • E. A theory that describes how galaxies evolved

Clicker Question Clicker Question

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SLIDE 13

What is the theory of General What is the theory of General Relativity? Relativity?

  • A. A theory that describes gravity in terms of

forces between massive bodies

  • B. A theory that describes gravity in terms of

spacetime curvature

  • C. The most general theory of the Universe
  • D. A theory that describes the atom
  • E. A theory that describes how galaxies evolved

Clicker Question Clicker Question

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SLIDE 14

Black Holes Black Holes

Solutions to the Solutions to the Einstein Einstein’ ’s equations s equations

  • f General
  • f General

Relativity, describing how Relativity, describing how spacetime spacetime curves curves around bodies of a certain size and mass. around bodies of a certain size and mass. For a given size, the larger the mass, the larger the For a given size, the larger the mass, the larger the curvature of curvature of spacetime spacetime. .

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SLIDE 15

Black Hole: object whose escape Black Hole: object whose escape velocity is faster than the speed velocity is faster than the speed

  • f light---> can
  • f light---> can’

’t escape!! t escape!!

  • Event horizon

Event horizon (Schwarzschild radius) is the point at which escape velocity equals speed of light ~ 3 km for each solar mass in the BH

  • Inside this radius not even light can escape

– can fall in but never get out

  • We can’t see any light coming from inside

BLACK BLACK hole

  • NO hard surface!!

hard surface!!

– Event horizon is a “theoretical” point of no return

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SLIDE 16

Warping of Space by Gravity Warping of Space by Gravity

  • Gravity imposes

Gravity imposes curvature on space curvature on space – – light light’ ’s path through space will be s path through space will be “ “bent by gravity bent by gravity” ” – – within the event horizon, it cannot within the event horizon, it cannot climb out of the hole climb out of the hole

  • As matter approaches

As matter approaches event horizon event horizon… … – – tidal forces are tremendous tidal forces are tremendous – – object would be

  • bject would be “

“spaghettified spaghettified” ”

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SLIDE 17

An observer can see the back of her head!

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SLIDE 18

Can We Detect Black Holes? Can We Detect Black Holes?

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SLIDE 19

By Their Very Nature, Black By Their Very Nature, Black Holes Are Invisible! Holes Are Invisible!

  • But we can detect their

effects effects on nearby matter (stars, gas, etc.)

  • Astronomers look for

compact “X-ray binaries”

Criteria:

  • 1. “Invisible” star in binary

system is too massive to be white dwarf or neutron star

– Mass > 3 MSun

  • 2. Too small in radius to be a

normal star

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SLIDE 20

Cygnus X-1 Cygnus X-1: : Blue

Blue supergiant supergiant (strong winds) (strong winds) pours H + He onto pours H + He onto accretion disk of black hole accretion disk of black hole

Blue Blue supergiant supergiant Accretion disk Accretion disk

Stellar-size Stellar-size black hole black hole

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SLIDE 21

Questions on Black Holes? Questions on Black Holes?

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SLIDE 22

What is a Black Hole? What is a Black Hole?

  • A. A black star
  • B. A concentration of mass with a gravitational

field so strong that not even light can escape its grip

  • C. A white dwarf painted in black
  • D. The compact remnant of a low-mass star
  • E. A project that requires large effort with no

return

Clicker Question Clicker Question

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SLIDE 23

What is a Black Hole? What is a Black Hole?

  • A. A black star
  • B. A concentration of mass with a gravitational

field so strong that not even light can escape its grip

  • C. A white dwarf painted in black
  • D. The compact remnant of a low-mass star
  • E. A project that requires large effort with no

return

Clicker Question Clicker Question

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SLIDE 24

GAMMA-RAY BURSTS: witnessing the birth of a new Black Hole in the Universe

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SLIDE 25

How it all started….. mid 1960s: VELA satellite … looking for signs of nuclear tests…

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SLIDE 26

TYPICAL GAMMA-RAY BURST

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SLIDE 27

Most GRB data gathered by BATSE in the 1990s

Main properties of GRBs: Rates: about 1 per day Durations: from tens of milliseconds to several hundreds of seconds, with bimodal distribution Highly variable

Short Long

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SLIDE 28

March 2003: a “special”, very energetic supernova (HYPERNOVA) is found coincident with the position

  • f the (long) GRB

Long GRBs are produced by the collapse of a massive star into a Black Hole!!

High star rotation likely needed

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SLIDE 29
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SLIDE 30

Several pieces of evidence seem to indicate that… …Short Gamma-Ray bursts are likely the result of a merger of two compact objects (i.e. NS-NS, NS-BH) Stay tuned as more observations come in…..

[Image from http://www.laeff.esa.es/BOOTES/esp/grb/grb4.htm]

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SLIDE 31
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SLIDE 32

What is a Gamma-Ray Burst? What is a Gamma-Ray Burst?

  • A. An energetic burst of gamma rays from the

center of the Milky Way.

  • B. An energetic burst of gamma rays from

distant galaxies.

  • C. The sign that a new star is born.
  • D. A sign of extraterrestrial life.
  • E. A burst of gamma-rays with duration between

1000 seconds and 1 day

Clicker Question Clicker Question

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SLIDE 33

What is a Gamma-Ray Burst? What is a Gamma-Ray Burst?

  • A. An energetic burst of gamma rays from the

center of the Milky Way.

  • B. An energetic burst of gamma rays from

distant galaxies.

  • C. The sign that a new star is born.
  • D. A sign of extraterrestrial life.
  • E. A burst of gamma-rays with duration between

1000 seconds and 1 day

Clicker Question Clicker Question

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SLIDE 34

What is the likely origin of a What is the likely origin of a long long-

  • duration Gamma-Ray Burst?

duration Gamma-Ray Burst?

  • A. The merger of two neutron stars.
  • B. The merger of a neutron star and a

black hole.

  • C. The collapse of a massive, rapidly

rotating star.

  • D. The collapse of a low-mass star.
  • E. The merger of two neutron stars or a

neutron star and a black hole. Clicker Question Clicker Question

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SLIDE 35

What is the likely origin of a What is the likely origin of a long long-

  • duration Gamma-Ray Burst?

duration Gamma-Ray Burst?

  • A. The merger of two neutron stars.
  • B. The merger of a neutron star and a

black hole.

  • C. The collapse of a massive, rapidly

rotating star.

  • D. The collapse of a low-mass star.
  • E. The merger of two neutron stars or a

neutron star and a black hole. Clicker Question Clicker Question

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SLIDE 36

What is the likely origin of a What is the likely origin of a short short-

  • duration Gamma-Ray Burst?

duration Gamma-Ray Burst?

  • A. The merger of two neutron stars.
  • B. The merger of a neutron star and a

black hole.

  • C. The collapse of a massive, rapidly

rotating star.

  • D. The collapse of a low-mass star.
  • E. The merger of two neutron stars or a

neutron star and a black hole. Clicker Question Clicker Question

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SLIDE 37

What is the likely origin of a What is the likely origin of a short short-

  • duration Gamma-Ray Burst?

duration Gamma-Ray Burst?

  • A. The merger of two neutron stars.
  • B. The merger of a neutron star and a

black hole.

  • C. The collapse of a massive, rapidly

rotating star.

  • D. The collapse of a low-mass star.
  • E. The merger of two neutron stars or a

neutron star and a black hole. Clicker Question Clicker Question