Galaxies – please review previous lectures on galaxies Phys 1830: Lecture 33 Yes there is a class on Friday and a quiz. Imaging workshop Weds 5:30pm in Allen 536 M82 by Remi Lacasse Office Hours: Monday 3pm i.e. TODAY Allen 514 Galactic wind i.e. fountain Previous Classes: pulsars, gamma-ray bursts Black holes This Class Black hole Milky Way Black Hole Galaxies – please review previous lectures on galaxies Upcoming classes Galaxies Cosmology Astronomy as a career ALL NOTES COPYRIGHT JAYANNE ENGLISH White Dwarfs

Black Holes: Can anything escape a black hole? 1. E.g. Roger Blandford: Mechanical energy can escape. Threaded through the gas, in the accretion disk and falling into the black hole, are magnetic field lines. The lines twist around the rotating black hole, slowing it down. The energy of rotation travels out along the lines and is deposited in the disk  explains X-ray hot spots. Use a scarf and tug on it. The energy of the tug travelling through the scarf is mechanical energy.

Black Holes: Can anything escape a black hole? 2. Hawking Radiation: A Quantum Mechanical effect due to the Heisenberg Uncertainty Principle. Even a vacuum has fluctuations: Pairs of virtual particles appear to together at some position in spacetime, move apart, come back together and annihilate. - If close to a black hole, one of the pair falls into it and the other member can escape to infinity, becoming a real particle. Uncertainty Principle: both velocity and position cannot be well defined. Although virtual particles appear and annihilate too quickly to be observed, their effects are observed. E.g. in particle accelerators. This is called the Casimir Effect The infalling member deposits negative energy into the black hole. .

Black Holes: Can anything escape a black hole? 2. Hawking Radiation: Radiation with a black body temperature inversely proportional to the black hole mass. Small black holes have higher temperatures. As the black hole radiates, it becomes smaller, temperature increases and it radiates faster. Black holes evaporate! A few solar mass black hole will has a temperature about 1 millionth of a degree above absolute zero.

What can escape from a black hole? Light and matter. Light and mechanical energy. Matter and mechanical energy. Hawking radiation and mechanical energy. Hawking radiation and light.

Types of Black Holes Type Mass Rsch Location Detection Method Lifetime Solar Masses yrs Supermassive >3*10**6 1/2 light-min Centre of Galaxies Doppler shift of orbiting 10**97 to 10**106 gas or stars. Period of orbit of stars in images. Mid-mass 500-5000 smaller than Globular Clusters Doppler shift (Intermediate) the solar radius X-rays from accretion. Stellar Mass 1 to 10 3 to 30 km Throughout disk Doppler Shift of companion. around 10**67 of galaxies Gravitational lenses. Primordial less than 1 1 cm Throughout universe Gamma-rays if around 10**10 evaporating but this is the only type of black hole that has not been observed even indirectly. Come in all sizes. (Note – a googol is 10**100 and 10**googol is called googolplex.) Primordial BH form in fluctuations at the beginning of the Big Bang. Created by compression of matter by external forces (pressure) in the early universe. All types of BH are rare.

Intermediate Black Holes. Formation by mergers of stars. Types of Black Holes: M 13 Danny Lee Russell Intermediate Black Holes. Formation by mergers of stars. Globular cluster has about a 1 million stars within several pc. Star density high in globular clusters so more opportunity for the merger of stars.

Types of Black Holes: Supermassive Black Holes Measure the motion of stars or gas (using spectra) in the centre of galaxies. Become an astronomer and figure this out! Supermassive Black Holes Centres of Galaxies (including Milky Way) In both spirals and ellipticals. If the bulge is small and featureless then there is no evidence that there is a black hole. Do galaxies form around black holes? Or do galaxies form and in the centre black holes accumulate? This is a question of current research.

Black hole in Our Milky Way Galactic Center Close-Up (a) An infrared image of part of the Galactic plane shows many bright stars packed into a relatively small volume surrounding the Galactic center (white box). The average density of matter in this boxed region is estimated to be about a million times that in the solar neighborhood. (b) The central portion of our Galaxy, as observed in the radio part of the spectrum. This image shows a region about 100 pc across surrounding the Galactic center (which lies within the bright blob at the bottom right). The long-wavelength radio emission cuts through the Galaxy's dust, providing a view of matter in the immediate vicinity of the Galaxy's center. (c) A recent Chandra image showing the relation of a hot supernova remnant (red) and Sgr A*, the suspected black hole at the very center of our Galaxy. (d) The spiral pattern of radio emission arising from Sagittarius A itself suggests a rotating ring of matter only a few parsecs across. All images are false-color, since they lie outside the visible spectrum. (SST; NRAO; NASA) Strong radio continuum emission in the centre of our Milky Way. Sgr A* (pronounced Sagittarius A star – it is NOT a star) has a rotating ring of matter only a few pc across

Black hole in Our Milky Way Use IR wavelengths to see through the dust. Measure the orbits of stars near Sgr A*

Black hole in Our Milky Way Compare the semi-major axis with the Kuiper Belt which extends a few hundred AU and the Oort Cloud which starts at 50,000 AU. The closest approach distance is within the Kuiper Belt. Orbits Near the Galactic Center This extremely close-up map of the Galactic center (left) was obtained by infrared adaptive optics, resulting in an ultra-high-resolution image of the innermost 0.1 pc of the Milky Way. The resolution is high enough that the orbits of individual stars can be tracked with confidence around a still-unseen Sgr A* (marked with a cross). The inset shows the orbit of the innermost star in the frame, labeled S2, between 1992 and 2003. The solid line shows the best-fitting orbit for S2 around a black hole of 3.7 million solar masses, located at Sgr A*. (ESO) The semi-major axis is 950AU and the closest approach is about 110 AU (about 15 lt-hr). Orbital velocity of star is from the circumference of the orbit divided by the period of the orbit. Setting F_orbit = F_ gravity  v**2 = GM/r re-arranged for mass M = r * v**2 / G

Black hole in Our Milky Way Globular cluster radii are more than several pc. (If you could magically force the stars in a globular cluster together to fit in this space, that would cause them to merge and form a massive black hole.)  3.7 million solar masses at the position of Sgr A* The only thing that fits within the volume of our solar system that has that amount of mass is a black hole. The Rsch ~3km * 3.7 * 10**6 ~ 10 million km (~10 times radius of sun) 0.02 AU (Mercury’s closest approach is 0.31 AU)

Jet from the Black Hole in the Milky Way http://chandra.si.edu/photo/2013/sgra/ Magenta: Chandra X-ray data Blue: VLA Radio data

Calculate this!!! Since our sun goes around the centre of our Milky Way Galaxy, how long does it take to orbit? Radius of orbit is 8.5 kpc and velocity = 220 km/s. 1 pc = 3.09 * 10**13 km

stars near the centre of the Milky Way are disappearing. Review: Astronomers conclude that a black hole resides in the centre of our Milky Way because: stars near the centre of the Milky Way are disappearing. no stars can be seen in the vicinity of the Galactic centre. stars near the centre of the Mily Way have been observed orbiting some unseen object. the Galaxy rotates faster than astronomers would expect.

Review Black holes only form when a very massive star implodes. The core of such a star is about 1 solar mass and therefore the black hole consists of singularity with this mass surrounded by an event horizon. True False

Want to help find black holes? www.blackholehunter.org Citizen science project. Questions? Discussion?

Galaxies harbour black holes HST & eVLA http://heritage.stsci.edu/2012/47/fast_facts.html 1.5 * 10**6 ly long! synchrotron emission Black holes –active galactic nucleus has a BH engine that generates jets which end in lobes (seen in radio continuum)

Galaxies harbour black holes Black holes – notice the jet in M87  existence of a black hole Measure the motion of stars or gas (using spectra) in the centre of galaxies  supermassive black holes. Become an astronomer and figure this out!

Sizes range from several million stars up to 100 billion stars. Galaxies: Definition: A large group of stars held together by the stars’ mutual gravitational attraction. Sizes range from several million stars up to 100 billion stars.

Spiral galaxies also contain significant amounts of gas and dust.

Galaxies: Gravitational Lensing Rotation Curves of Spirals (Dark matter review on the overhead projector.) Using these techniques we can measure the amount of dark matter in a galaxy. That is, we compare the dynamical mass and the luminous mass. A major component of galaxies (90%) is dark matter. (around Lecture 14.)

The rings are from 2 galaxies behind the foreground galaxy. Can determine that there is dark matter using GR, rather than Newton’s law (i.e. rotation curve). The rings are from 2 galaxies behind the foreground galaxy. Foreground galaxy has been subtracted from image on the right. “This is an image of gravitational lens system SDSSJ0946+1006 as photographed by Hubble Space Telescope's Advanced Camera for Surveys. The gravitational field of an elliptical galaxy warps the light of two galaxies exactly behind it. The massive foreground galaxy is almost perfectly aligned in the sky with two background galaxies at different distances. The foreground galaxy is 3 billion light-years away, the inner ring and outer ring are comprised of multiple images of two galaxies at a distance of 6 and approximately 11 billion light-years. The odds of seeing such a special alignment are estimated to be 1 in 10,000. The right panel is a zoom onto the lens showing two concentric partial ring-like structures after subtracting the glare of the central, foreground galaxy.”

Gravitational Lensing in the submm! Atacama Large Millimetre/Submillimetre Array

Credit: Dan Marrone “Baby Boom” Can also use lensing to find out other characteristics of galaxies, e.g. very young dusty, gassy galaxies. Milky Way forms 1-10 stars a year. These “starburst” galaxies form up to 10,000 stars per year. The background galaxy (coloured pink) is about 12 billion light years away. This wavelength traces gas & dust  means that rapid star formation began a mere two billion years after the Big Bang.

What could dark matter be? ~10% of matter is is sufficiently luminous to be detected Stars X-ray gas in clusters of galaxies Dust HI gas Discuss briefly with your neighbours what 90% of the rest of the matter could be.

What could dark matter be? From measurements we estimate: ~20% from dim, distant objects made from normal atoms Very cold gas Black holes Planets Small stars like Brown Dwarfs ~10-20% are exotic particles called neutrinos Recall neutrinos are created in the proton-proton chain.

What could dark matter be? The rest is expected to be exotic particles. (e.g. Sudbury Neutrino Observatory is converting its apparatus to look for these.)

No one has determined what could be dark matter No one has determined what could be dark matter. Planets, dwarf stars, black holes, very cold HI gas have all been eliminated as candidates. a) True b) False

Galaxies: Hubble Tuning Fork Diagram Note at the joint of the branches there is a “spheroidal” galaxy. Main types are Elliptical (E) Spiral (S or SB, if they have a bar.) Irregular (Irr)

Population II and old Population I stars (i.e. old stars). Galaxies: Elliptical 20% of observed galaxies (not including faint, distant dwarf ellipticals). Population II and old Population I stars (i.e. old stars). Mass: 10**5 to 10**13 solar masses Luminosity: 3 * 10**5 to 10**11 solar L Stars in orbit but orbits are at random orientations. Note ** means “to the power”. Miniscule amount of gas and dust.

Leo I: A low surface brightness dwarf galaxy with a spheroidal shape. Galaxies: Elliptical Miniscule amount of gas and dust. Leo I: A low surface brightness dwarf galaxy with a spheroidal shape.