Stranger Things in our Universe - University of New...
Transcript of Stranger Things in our Universe - University of New...
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Stranger Things
in our UniverseLecture 20
4/9/2018
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April 1311:00am room 190 Physics and Astronomy
Lin Yan (IPAC/Caltech)
Superluminous Supernovae After A Decade of
Study
Location: Socorro DSOC Auditorium (Broadcast to CV, GB)
Local Host: Amy Kimball
https://science.nrao.edu/facilities/vla/ctw/coll
Extra Credit Opportunity
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WHEN’S THE NEXT TEST ?!?!?!?
• The test will be on April 11th (a week from today)
• Topics will include:• The Sun
• Measuring the Stars
• Interstellar medium
• Star Evolution
• Star Death
• Obstacle course for extra credit-any injures will result in F
• Review Tuesday from 3-5 in room 5 physics and astronomy.
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Type II supernovae-Core Collapse Super Novae
• Hydrostatic equilibrium is lost because Iron does not burn.
• Before this point core was held up by electron degeneracy pressure and nuclear fusion.
• Core is compressed, due to gravity, by overlying layers.
• Electron degeneracy pressure is not strong enough and the core collapses, compressing objects even further.
• Photodisintegration occurs and many neutrons are created as heavy nuclei are ripped apart.
• Neutrons get squeezed inside of the core.
• Collapsing star is halted by neutron degeneracy pressure, resulting in a violent, fast, rebound of the collapsing material.
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Neutron Stars
• If initial mass of the star is between 8 and 25 solar masses, the core collapse supernova will leave behind a neutron star.
• Densest type of stars in the universe (1017 kg/m3) and smallest stars (20 km) in the universe. Roughly diameter of Albuquerque (west side to the east mountains).
• Because so much mass is packed into such a small core, the surface gravity of the star is immense. 150 lb person would weight 1 million tons.
• Extremely hot surface at ~700,000 Kelvin (surface of the sun is 6000 Kelvin).
• Incredible strong magnetic field.
• What is holding it together?
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Neutron Stars and Conservation of Angular Momentum
• Remember that due to conservation of angular momentum, as large spinning objects compress to smaller spinning object, they rotate faster.
• Neutron Stars rotate incredibly fast because the massive red giant’s angular momentum has been transferred to the tiny neutron star.
• Some neutron stars are spinning at roughly 20% of the speed of light.
• The fastest man made object has gone roughly 0.02% of the speed of light.
• How do we observe neutron stars since they are so tiny?
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Pulsars• The fast rotation and strong
magnetic field of a neutron stars, accelerate charged particles along their magnetic field lines emitting huge amounts of radiation.
• Radiation is emitted in a tight beam along the magnetic axis.
• Even though the star is not very bright, these beams of radiation are very intense and can been seen at very long distances
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Lighthouse beacon
• Each pulsar is unique, but typically they pulse anywhere between every second to every millisecond.
• This pulsing allows for us to measure the rate at which the object is rotating.
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The Crab Pulsar
ChandraX-rayimage
On
Off
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Pulsars are incredibly accurate clocks!
• Example: period of the first discovered millisecond pulsar is: P=0.00155780644887275 sec
• It is slowing down at a rate of: 1.051054 x 10-19 sec/sec
• Where does the energy go? Heating of surrounding material.
• Some of the first exoplanets were discovered by measuring the perturbation of pulsar periods. Similar to measuring the Doppler shift of stars due to exoplanets.
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Pulsar Exotica
• Unlike the Sun, neutron stars do not rotate differentially.
• Matter can flow without friction, a condition called superfluidity.
• Core may be made up of quarks, the fundamental particles that make up all protons and neutrons
Strange subatomic particles
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Neutron Stars and Pulsars
• All pulsars are neutrons stars.
• Not all pulsars are neutron stars.
• Pulsars stop pulsing in a few million years
• For every pulsar we know of, there are a few 1000 that we will never see.
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X-Ray Bursts
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Black Holes
• What happens when gravity overcomes neutron degeneracy pressure?
• A object so dense is created that not even light cannot escape the gravitational pull of these objects.
• This is the fate of stars that are roughly 25 times more massive than our Sun.
• Black holes are defined by three physical properties:• Mass
• Spin
• Electric charge
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The general theory of relativity is our most accurate description of gravitation
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Event Horizon and Schwarzschild Radius
• How fast does an object need to be traveling in order to escape the gravitational force of an other object? • Escape Velocity!
• The farther from an object, the lower the escape velocity.• Why?
• The Schwarzschild radius is defined as the radius around a black hole at which the escape velocity is equal to the speed of light.
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Black Hole Evidence
• Astronomers have found convincing evidence for a supermassive black hole in the center of our own Milky Way galaxy.
• Scientists verified the existence of the black holes by studying the speed of the clouds of gas orbiting those regions.
• Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system.
• Black holes typically start out with a mass of a few solar masses. They continue to grow as they absorb more matter.
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• Black holes can be very bright and good source for gamma rays and x-rays. Cyngus X-1 is an example of this.
• Black holes rotate at a very high speed thus it takes a very long time for objects to fall into the black hole.
• As gas rotates, it gets incredibly hot (and bright), making black holes some of the brightest objects.
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black hole binary system discovered by UNM graduate student Karishma Bansal (2017)
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Gravitational Lensing
AB
AB
What is the fastest path between point A and B?1. A Straight line?2. A Curved line?
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Gravitational Waves
• Massive binary rotating systems can create waves in spacetime.
• Radiate energy just like electromagnetic waves.
• Can measure them by looking local shifts in spacetime.
• In 2017 the LIGO collaboration detected these waves win the Nobel prize.
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Light in a gravity well
• Just like climbing a mountain, as light climbs out of a gravity well it loses energy.
• Since light is traveling at a constant speed of c, it cannot slow down. Rather, it increases it’s wavelength (loses energy).
• Increasing wavelength implies a longer period for a light wave.
• The deeper in a gravity well you are, the faster you experience time!
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Falling into a black hole is an infinite voyage
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Black holes evaporate