Life After Stellar Death

Transcription

1 Life After Stellar Death Supernovae, Neutron Stars, Pulsars and Black Holes Edward P.J.van den Heuvel KITP, March Universiteit van Amsterdam The Netherlands

2 Age of the Universe: 13.7 billion years Age of our Milky Way Galaxy: at least 13 billion years Age of our Solar System and Earth: 4.65 billion years Hydrogen (H) and helium (He) were made in the Big Bang, all other elements were made in earlier generations of (massive) stars We are made of Stardust

3 Sun and planets on the same scale x Mass of Earth 70% Hydrogen, 28% Helium, 2% heavier elements

4 Sun and Planets to the same scale Mass: Times Earth 70% Hydrogen 28% Helium 2% Heavier elements

5

6

7 Orion Distances in lightyears Betelgeuze 420 lyr Bellatrix 250 Alnilam 2000 lightyrs Saiph 750 Rigel 800

8 Velocity of light is finite: Km/second FAR AWAY = LONG AGO

9 Sun orbits galactic Center once every 220 million years. went 21 times around since birth of solar system Diameter: lightyears Over 100 billion stars like our sun YOU ARE HERE Sun is lightyrs from Galactic center

10 Andromeda Nebula: 2 million lightyrs

11 Galaxy NGC 1232 Distance 65 million lightyears

12 Sun emits in Energy: Watts 26 = 4.10 Watts (= Joules/second) One second is enough for energy consumption of the world population for about 1 million years One two-billionth is intercepted by Earth: Still some ten thousand times the human energy consumption

13 + proton = nucleus of Hydrogen atom neutron: practically the same mass as proton + + nucleus of Helium atom (2 protons and 2 neutrons, mass: (1/134)th less than 4 protons In fusing 4 protons into 1 helium nucleus, (1/134)th of mass is lost: converted into energy according to Einstein s formula: E = M c² Required temperature inside the star: million K Fusion of 1 gram of Hydrogen yields enough energy to drive a middle-size car once around the Earth ( km)

14 To generate its energy, the Sun burns (fuses) 600 million tons of Hydrogen per second 4 million tons of this matter per second is converted into pure energy and radiated out

15 LIFETIME OF A STAR: TIME REQUIRED TO BURN ALL ITS NUCLEAR FUEL (HYDROGEN= 70% OF ITS MASS) SUN: 10 BILLION YRS PRESENT AGE: 4.65 BILLION YEARS STAR OF 25 SOLAR MASSES: BURNS ITS FUEL TIMES FASTER: LIVES 2000 TIMES SHORTER: 5 MILLION YEARS

16 Rosette Nebula Cluster with stars of about 25 solar masses

17 Sirius B discovered in 1862 by Alvan Clark - is times fainter than Sirius A. They orbit each other in 50 years. In 1910 it was discovered: the mass of Sirius A is TWO Solar masses, that of B is ONE Solar mass, but it has same size as EARTH!.

18 Already more than white dwarfs known in Galaxy (From nr. 10 on some 6700 discovered by Willem Luyten( )

19 Hydrogen atom + - electron Atom held together because + and electric charges strongly attract each other, proton + Diameter of smallest electronorbit: times larger than diameter of atomic nucleus: Volume can be compressed ( 50000)³ times density hundred trillion times larger. 30 Requires Pressure of 10 Bar neutron (anti-)neutrino Proton and neutron are ~ 1840 times heavier than electron, neutrino wheighs practically nothing Pressure in center of White Dwarf is only Bar (in Sun: 10 Bar) 18

20 Normal matter: smallest stable electron orbits undisturbed White Dwarf is burned-out, dead star: Nuclei of He,C and O Electron-Degenerate matter:nuclei closer together than diameter smallest stable electron orbits: Electrons form very-high-pressure Fermi gas (Quantum gas) At not too High temperature

21 Collapses White Dwarfs ( ) Chandrasekhar-limit (1930, Nobelprize 1983) Neutron Stars Radii of white dwarfs and neutron stars of increasing mass, in solar masses

22 Neutron star: times mass of Earth in a sphere of 20 km (12 Miles) diameter Accelleration of gravity g = 100 billion times that on Earth Escape velocity from surface = 0.5c = km/sec (from Earth: 11.2 km/sec) Neutron star: pit with a bottom; light can still escape (Oppenheimer and Volkoff 1938) Black Hole: no bottom (Oppenheimer and Snyder 1939)

23 Energy liberated in collapse to neutron star of mass M: M falls inwards with velocity 0.5c and is then suddenly stopped: 2 2 Ekinetic = 0.5 M(velocity) = (1/8)Mc =0.125Mc² As much energy as the Sun emits in 1000 billion years (100 times its life)! W.Baade &F.Zwicky(1934): Supernova is caused by collapse of stellar core to a neutron star Infall velocity = 0.5c = km/sec

24 SN 1998aq in NGC 3982 (22/23April 1998, Nordic Telescope La Palma,V+I) During three weeks a billion times brighter than the Sun

25 SN1994D SN2003cg A billion times brighter than the Sun One observes on average in galaxies like ours ONE supernova per 30 to 100 years. By monitoring thousands of galaxies per year one discovers many tens of new Supernovae per year

26 SNR 1572 (Tycho) Chandra 0.1-2KeV W39B 2 arc min In our Galaxy we find hundreds of shells of Supernovae that exploded during the past years. Young shells expand with velocities of 1500 to km/sec. Older ones have swept up interstellar gas, which slowed down their expansion rates.

27 Crab Nebula, ESO-VLT Remnant of Supernova 1054 AD, recorded by Chinese, Korean, Japanese and Iranian astronomers Distance 5000 lightyrs Expansion velocity ~1500km/s

28 Nov.1967: Student Jocelyn Bell discovers the first pulsar CP 1919, regularly pulsing radio source with P=1.33 sec First thought: Little Green Men Such a period is just possible for a vibrating or rapidly rotating White Dwarf, but faster is impossible for White Dwarf A Neutron star has a vibration period and shortest possible rotation-period of about ONE THOUSANDTH of a second!

29 Crab Nebula in blue light; Nov 1968: radio pulsar discovered by two American radio astronomers: period seconds ( 1/30 th of a sec

30 Radio pulsar in Crab Nebula is also a VISIBLE STAR that flashes on and off 30 times per second! Only a rotating neutron star can explain this pulse period! Optical pulses of Crab Pulsar (P= sec)

31 Lighthouse model of a Pulsar

32 12 miles (20 km) Mass: about times Earth (1,3 times the Sun) Density: 10 to 10 times water Slowing down of rotation: Magnetic field 10 to 10 that of Earth times

33 Crab Nebula Blue light NASA s Chandra observatory Chandra: X-ray picture Energy Output: times Sun

34 Crab Nebula Chandra X-ray Space telescope time-lapse movie

35 From Joddrel Bank Radio Observatory PSR B , P= seconds Vela Pulsar PSR B , P= sec. (11 pulses per second) Crab Pulsar PSR B P= seconds (30 pulses per second) PSR B , P = seconds (642 pulses per second)

36

37 Sun Galactic Center Positions of the about 1800 known radio pulsars on the Galactic plane

38

39

40 STAR OF ABOUT 20 SOLAR MASSES, SHORTLY BEFORE THE COLLAPSE OF ITS BURNED-OUT CORE AGE: 7 MILLION YEARS

41 FINAL STAGES OF STARS KM BELOW 8 SOLAR MASSES EARTH WHITE DWARF EARTH MASSES BETWEEN 8 AND ~ SOLAR MASSES LIVE SHORTER THAN 20 MILLION YEARS NEU- TRON STAR EARTH MASSES 20 km MORE MASSIVE THAN ~ 25 SOLAR MASSES LIVE SHORTER THAN 6 MILLION YEARS 1 MILLION EARTH MASSES BLACK HOLE

42 Black-Hole X-ray Binary (about 30 known in our Galaxy)

43 Summary Life After Stellar Death can be very interesting: - White dwarf - Pulsar = Neutron star - Black hole (in a binary: strong X-ray source) - Double Neutron stars: sources of gravitational waves and Short Gamma-ray Bursts Furthermore: - The gold in your wedding ring, - The calcium in your bones, - The silicon in your computer-chip - The phosphorus in your brains, and 83 of the 84 other elements than Hydrogen and Helium Would not have existed without Supernovae and Neutron Stars

44 Planetary nebula In Aquarius Outflow velocities a few km/sec (not explosive) Central star is a very hot white dwarf!

45 Planetary Nebula : Central star is very hot White Dwarf