Supernova Remnants

Key points: Observational evidence for neutron stars, origin of elements, collapse of stellar cores; cosmic cycle of material

Most of what we know about supernova remnants has been learned from a few examples that exploded recently and are relatively close, as we discuss below.

Supernova 1987a

In February, 1987, a star exploded as a supernova in the Large Magellanic Cloud, a small companion galaxy to the Milky Way.

"Before" to the immediate left and "after" to the far left.from http://heasarc.gsfc.nasa.gov/docs/xte/xte_images.html

This is the closest supernova to have gone off since Cas A about 320 years ago.

We learned many details of the supernova process by studying 1987a:

graph of neutrino counts shows a peak from SN 1987A  

In fact, about 10 billion neutrinos passed through each of you (or your parents)! Fortunately, they do not react easily.

(from http://hyperphysics.phy-astr.gsu.edu/hbase/astro/sn87a.html)

neutronstara.gif (235229 bytes) The neutrinos are generated in the last stages of the collapse leading to the supernova, where electrons and protons merge at the high pressure and temperature, and produce neutrons and neutrinos. (animation by G. Rieke.)
SN 1987A precursor star was a blue supergiant From SN 1987a, we learned that the character of a supernova may depend on the type of star exploding -- most supernovae were though to be red supergiants just before the explosion while 1987a was a blue supergiant

(from G. Smith, http://casswww.ucsd.edu/public/tutorial/SN.html)

light curve decay matches the half lives of nickel and cobalt The rate the luminosity decreased after the explosion was the result of radioactive decay of elements produced in the explosion, particularly nickel and cobalt.

The supernova produced enough cobalt to make 20,000 earths entirely of this element!

(From Chaisson & McMillan, Astronomy Today)

HST image of rings of material ejected by SN 1987A  

Prior to the explosion, material appears to have been ejected in two opposite pointing cones. When the blast of light from the explosion overtook these cones, it lit up the two large ellipses projected against the sky in the top part of the picture.

Below, we can see subtle image shape changes showing the material expelled by the explosion. This hot gas is moving at about 1% of the speed of light, so these features are about 100 times smaller than the ellipses lit up by the light.

 

We could watch shock waves propagate outward and see the beginning of the formation of the supernova remnant nebula (from http://apod.nasa.gov/apod/ap120227.html, NASA, ESA, Makr McDonald).

More on SN 1987A at: http://heritage.stsci.edu/public/feb4/sn1987anino.html

Cas A

casaall.jpg (93132 bytes) Image of the 320-year-old supernova, Cas A. This lovely composite image shows the infrared in red, optical in yellow, low-energy x-ray in green, and high-energy x-ray in blue. The infrared traces tiny heated dust particles. The grains are made of simple silicates and aluminum oxide, minerals that are the building blocks for rocks on Earth (and ones that can survive in the harsh environment in the supernova remnant).  The optical shows where there are emission lines from gas, and the x-ray traces very hot gas.There is remarkable structure in the debris of a gigantic stellar explosion, as well as an enigmatic source in the center, which could be a rapidly spinning neutron star or black hole. This image shows the later development of a remnant like that around SN1987a. (from O. Krause, G. Rieke, Spitzer Science Center, Caltech/JPL)

The Crab Nebula

The supernova that produced the Crab Nebula was observed in 1054 A.D. by Chinese astronomers -- knowing the actual year of the explosion has enabled a greater understanding of this pulsar and supernova remnant. The remnant is below as seen in the optical (to the left the whole nebula and to the right its core).

groundbased and HST pictures of the Crab Nebula

radio image of the Crab Nebula The radio structure is very similar to that in the optical. Most supernova remnants are thin and wispy -- why is the Crab so energetic?   (from NRAO/VLA)  
HST image of wispy gas around Crab pulsar           The energy is renewed continuously by a powerful pulsar at the center of the nebula.pulsarmovie.gif (150360 bytes)  crbpuls1.gif (10993 bytes)

crbpuls.gif (347141 bytes)

"stars" are numbered above to match the numbering in the picture to the left

The "star" near the center   (the lower of the two to the left in this picture) is actually a very rapidly rotating pulsar -- the remainder of the massive star that exploded. Animation by G. Rieke, from data obtained by N.A.Sharp/AURA/NOAO/NSF http://www.seds.org/messier/more/m001_pulsar.html
animation of gas motions near the pulsar This animation based on a series of HST images shows energy from the pulsar whipping up the nebula around it and keeping it energized -- including with the energetic sea of electrons that makes it glow.

The animation starts with the view in the still to the upper right and then zooms in and zooms again until you are looking just at the pulsar.

crabxrayopt.jpg (233902 bytes)  

In the X-ray, the view is dominated by the activity driven by the pulsar. In this composite picture, X-rays are blue and optical light (from the HST images above) in red. (from J. Hester et al., HAT/NASA via astronomy picture of the day, http://antwrp.gsfc.nasa.gov/apod/ap050326.html)

crabpuls.gif (366749 bytes) This animation starts with the image above (rotated a bit) and locates the pulsar and a shock front. It then zooms in, pauses briefly, and then runs through a short sequence of X-ray images that show the shock moving outward through the hot gas in a ring surrounding the pulsar. This is the way the pulsar energy escapes to power the nebula. From Chandra Photo Album, http://chandra.harvard.edu/photo/category/quasars.html Models that fit the image show this behavior more clearly for comparison with the image, plus two jets coming out in opposite directions and perpendicular to the ringen00500_1.jpg (18578 bytes).(reload to restart lecture animations)

The Crab Nebula pulsar is one of the fastest (and we now know therefore youngest) pulsars known.

Aging supernova remnants

 

 

 

 

 

 

As supernova remnants age, they expand into interstellar space and deposit material highly enriched in heavy elements into the surrounding space. This picture shows a part of the material thrown off by a supernova that exploded about 10,000 years ago to form the Veil Nebula. (from APOD, http://apod.nasa.gov/apod/ap130529.html, Martin Pugh)

 

 

 

 

 

 

 

 

wisps in the Cygnus loop remnant Spectra of the remnants show that the outer layers of the star, rich in silicon, oxygen, and carbon, are ejected at high velocities (10,000 - 20,000 km/sec).

The spectra show that heavy elements (heavier than iron) created during the supernova explosion are also ejected.

As a result, supernova explosions are the main source for heavy elements (hence, your own body contains atoms that came from a supernova explosion!)

"All of us are truly and literally a little bit of stardust."

- William A. Fowler (Nobel Prize, 1983)

Summary: Cycles of Matter: Where the Heavy Elements Come From

cycles2.jpg (232158 bytes) Starting from the the upper left. interstellar material compresses into high density clouds mostly of molecular hydrogen where stars and planets form (upper right). The massive stars rapidly run through their main sequence lifetimes (lower right), building up heavy elements, and then explode as supernovae (bottom center). The heavy elements in their  interiors escape in these explosions, and more are made during the explosions themselves. The enriched remnants of these stars expand into the interstellar medium (lower left) and merge with the interstellar material to be swept up in the next cycle of star formation.(by G. Rieke, upper left from Spitzer Science Center, http://www.spitzer.caltech.edu/Media/releases/ssc2004-08/ssc2004-08a.shtml upper right by Don Dixon, http://www.cosmographica.com/gallery/ lower right from Voyager Project http://voyager.jpl.nasa.gov/multimedia/flash_html.html; center bottom from Chandra Science Center, http://chandra.harvard.edu/photo/2002/0237/0237_hand.html lower left from Space Telescope Science Center. http://www.spacetoday.org/DeepSpace/Telescopes/GreatObservatories/Hubble/

 

Where do the elements heavier than hydrogen and helium come frombutton.jpg (6796 bytes)

Test your understanding before going onbuttongrad.jpg (11232 bytes)

supernova-sm.gif (14736 bytes)

 

 

 

 

Simulation of effect of a nearby supernova on a star like the sun. http://www.pnl.gov/energyscience/

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An illustration from Chinese mythology of the Milky Way, from Postel & Guerrero http://www.artistexpo.com/Collprints.html

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