The Stellar Graveyard General Astronomy: Stars & Galaxies : ID - PowerPoint PPT Presentation

ASTR 1120 The Stellar Graveyard General Astronomy: Stars & Galaxies : � ID IDTERM # #2 � EXT � ursday 10/15: � EXT Tuesday 10/20: � � earching for dist stant world � � GO DIRECTLY TO THE PLANETARIUM When the mass is too great for even neutron degeneracy What’s In The Stellar Graveyard? to hold up… • Lower mass stars � white dwarfs – Gravity vs. electron degeneracy pressure when M core > 3 M sun • High mass stars � neutron stars – Gravity vs. neutron degeneracy pressure • Our supernova core collapses to an • Even more massive stars (M>30-40 M sun ) � black infinitely small point holes – Gravity wins � Black Hole

Black Holes – sort of courtesy of Albert GENERAL RELATIVITY : (in a nutshell) • Einstein’s (1911) General Theory of � asses �� � pace � m � Relativity: gravity is how � curve. really the warping of spacetime around an object with much mass � pace � m � , � i � it � � urvature, , �� s masse � • Light travels in “straight how � move. lines” – and its bending comes from spacetime being curved by gravity [Image from “Spacetime and Gravity” by S. Carroll] Effects of strong gravity on light can act like lens can redshift light [Image by R. Jantzen]

Two images of a distant quasar Source behind the lens: EINSTEIN RING A B [Image credit: R. Ellis & I. Smail with HST (NASA/STScI)] [Image credit: L. King with HST (NASA/STScI)] Clicker Question The arches What is the theory of General are the Relativity? result of gravitational A. A theory that describes gravity in terms of lensing 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 [Image credit: P. Natarajan with HST (NASA/STScI)]

Clicker Question Black Holes What is the theory of General Solutions to the Einstein’s equations of General Relativity? Relativity, describing how spacetime curves around bodies of a certain size and mass. A. A theory that describes gravity in terms of forces between massive bodies For a given size, the larger the mass, the larger the B. A theory that describes gravity in terms of curvature of spacetime. 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 Warping of Space by Gravity Black Hole: object whose escape velocity is faster than the speed of light---> can’t escape!! • Event horizon (Schwarzschild radius) is the point at which escape velocity equals speed of light ~ 3 km for each solar mass in the BH • Gravity imposes curvature on space – light’s path through space will be • Inside this radius not even light can escape “bent by gravity” – can fall in but never get out – within the event horizon, it cannot climb out of the hole • We can’t see any light coming from inside � • As matter approaches event horizon… BLACK hole – tidal forces are tremendous – object would be “spaghettified” • NO hard surface!! – Event horizon is a “theoretical” point of no return

Can We Detect Black Holes? An observer can see the back of her head! By Their Very Nature, Black Cygnus X-1: Blue supergiant (strong winds) pours H + He onto accretion disk of black hole Holes Are Invisible! • But we can detect their Stellar-size effects on nearby matter black hole (stars, gas, etc.) • Astronomers look for compact “X-ray binaries” Accretion disk Criteria: 1. “Invisible” star in binary system is too massive to be white dwarf or neutron star Mass > 3 M Sun – Blue supergiant 2. Too small in radius to be a normal star

Clicker Question Questions on Black Holes? 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 GAMMA-RAY BURSTS: witnessing the birth of a new Black Hole What is a Black Hole? in the Universe 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

TYPICAL GAMMA-RAY BURST How it all started….. mid 1960s: VELA satellite … looking for signs of nuclear tests… Most GRB data gathered March 2003: by BATSE in the 1990s a “special”, very energetic supernova Main properties of GRBs: (HYPERNOVA) Rates: about 1 per day is found coincident with the position Durations: from tens of milliseconds to several of the (long) GRB hundreds of seconds, with Long bimodal distribution Long GRBs are Short produced by the collapse of a massive Highly variable star into a Black Hole!! High star rotation likely needed

Several pieces of evidence seem to indicate that… [Image from http://www.laeff.esa.es/BOOTES/esp/grb/grb4.htm] … 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….. Clicker Question 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 What is the likely origin of a long - What is a Gamma-Ray Burst? duration Gamma-Ray Burst? A. The merger of two neutron stars. A. An energetic burst of gamma rays from the center of the Milky Way. B. The merger of a neutron star and a B. An energetic burst of gamma rays from black hole. distant galaxies. C. The collapse of a massive, rapidly C. The sign that a new star is born. rotating star. D. A sign of extraterrestrial life. D. The collapse of a low-mass star. E. A burst of gamma-rays with duration between E. The merger of two neutron stars or a 1000 seconds and 1 day neutron star and a black hole. Clicker Question Clicker Question What is the likely origin of a long - What is the likely origin of a short - duration Gamma-Ray Burst? duration Gamma-Ray Burst? A. The merger of two neutron stars. A. The merger of two neutron stars. B. The merger of a neutron star and a B. The merger of a neutron star and a black hole. black hole. C. The collapse of a massive, rapidly C. The collapse of a massive, rapidly rotating star. rotating star. D. The collapse of a low-mass star. D. The collapse of a low-mass star. E. The merger of two neutron stars or a E. The merger of two neutron stars or a neutron star and a black hole. neutron star and a black hole.

Clicker Question What is the likely origin of a short - 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.