Stranger Things

in our UniverseLecture 20

4/9/2018

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

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.

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.

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?

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?

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

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.

The Crab Pulsar

ChandraX-rayimage

On

Off

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.

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

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.

X-Ray Bursts

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

The general theory of relativity is our most accurate description of gravitation

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.

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.

• 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.

black hole binary system discovered by UNM graduate student Karishma Bansal (2017)

Gravitational Lensing

AB

AB

What is the fastest path between point A and B?1. A Straight line?2. A Curved line?

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.

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!

Falling into a black hole is an infinite voyage

Black holes evaporate