Novae and supernovae Szydagis 03.07.2018

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Artistic representation of a supernova in progress, from http://www.chinatopix.com

The guest stars

What is a nova?

�  Latin for ‘new.’ Referring to a new star appearing in night sky

�  A white dwarf star accretes hydrogen from a massive partner

�  Fresh outside layer of hydrogen gets compressed under the gravitational pressure (a function of depth) of its own mass, heating until fusion can begin anew in the star

�  However, a white dwarf does not have the correct structure and mass to maintain hydrostatic equilibrium

�  A thermonuclear blast occurs, akin to a giant hydrogen bomb in space, causing a brightening. Dwarf survives, cycle repeats

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An artist’s impression of a star system responsible for a nova. Photograph: David A. Hardy/www.astroart.org//PA

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Image Credit: NASA, ESA, and A. Feild (STScI); vectorisation by chris 論 - http://hubblesite.org/newscenter/archive/releases/star/supernova/2004/34/image/d/

�  Covered basics (last steps) already �  In context of

standard candle on cosmic distance ladder (Chapter 4b)

�  Main difference from a nova: brighter explosion, because star does *not* survive �  Replaced with a

black hole �  Caused by any

matter accruing

An Alternative Model

5/13 Image: GSFC / Dana Berry.

A two white-dwarf merger

(supernova classification does not refer to origins, about which we must theorize)

Type Ib, Ic, II Supernovae �  We already covered these in a previous class, but without

naming them. These are caused by a red SUPERgiant onion collapse and fireball, after iron core maximum scrunch

�  Distinguishable from Type 1a by the lack of single-ionized silicon absorption line. 1b possesses lines of helium that 1c lacks. Absorption & emission spectra tell us elements

�  Typical death of a massive star, leaving a neutron star or a black hole behind. (By contrast, red giant leaves behind a white dwarf, and a planetary nebula without supernova)

�  Type II (many subtypes) distinguishable by the presence of hydrogen, but same old, while “hypernovae” possibly caused by influx of matter into black hole, or hole merger

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Minkowski-Zwicky Classification Scheme, by absorption lines

Famous Supernovae �  Type II July 4, 1054, observed by the Chinese, that

led to the creation of the Crab Nebula and a pulsar

�  1604 Type Ia (in retrospect) observed by Kepler

�  Type II in 1987(A), whose neutrinos were detected by underground experiments in labs across world �  Occurred in Tarantula Nebula, in neighboring LMC

�  A supernova occurs only once or twice per century per galaxy is the rule of thumb. Can not predict

�  We can see the light from one that is even billions of light years away, especially if Type Ia. But neutrinos from close by (reduced flux plus harder to detect)

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Progression

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[NASA/HST, Z. Levay, B. Preston]

The rings seen around SN1987A by the Hubble Space Telescope were a big surprise and their origin is still a mystery. We suspect that the progenitor star was a binary star system that merged some 20,000 years before it exploded, ejecting the rings during the merger. The blast wave from the supernova explosion is just now beginning to hit the ring, causing a bright spot to appear. During the next ten years, the ring should become several hundred times brighter than it is today, giving us an opportunity to understand the mechanism by which the rings were ejected. [The video at the lower right.]

http://astronomy.nmsu.edu/geas/lectures/lecture25/slide02.html

A Review of Dwarfs and Giants

�  We have covered knowledge you require to answer

�  List every type of dwarf star and giant star you can come up with, and the properties or key features of each category (usually denoted by color)

�  Half of you, start with dwarfs and other half giants

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Origins of the Elements

�  Big Bang Nucleosynthesis (BBN) gives us a lots of hydrogen, some helium, and a smattering of the other lightest elements

�  The complex cores of red giant and supergiant stars give us many of the intermediate-mass elements, up through iron, via nuclear fusion. Hydrogen, helium, C, O, Ne, Mg, Si, S, Ni

�  A supernova blast gives us the rest of the elements, stable and radioactive, filling up the entire periodic table of naturally occurring elements all the way up through uranium (Z = 92)

�  r-process and s-process: we are all made up of star material!!

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A Luminous Red Nova?

�  A merger of two stars �  Typically main sequence though, not white dwarfs

�  Between a white dwarf nova and a supernova, which can outshine a galaxy, in terms of brightness

�  As with other stellar phenomena, sustain a certain characteristic brightness pattern

�  Characteristically red and infrared

�  Recent discovery: first announced only in 2007

�  Why red? Unknown!! 11/13

More to World Than Lights

�  Gamma ray bursts (GRBs) detectable by Fermi-LAT �  We will cover in “Particles From Space,” baby galaxies

�  X-ray pulsars, detected by Chandra observatory �  Same old story: infalling mass from partner again

�  Astrophysical masers (microwave laser-equivalents) �  Molecular clouds, atmospheres, even interstellar space

�  All the combinations of binary, trinary, etc. stars

�  Stellar winds eject mass at high speeds due to either high temperature or to direct radiation pressure

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Conclusion

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