Lab 6

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ASTR 264 LAB ACTIVITY 6: Stellar Evolution & Black Holes Part 1 – Stellar Evolution 1. Let’s try to organize the new terminology we’ve learned so we can better understand stellar evolution. The pattern by which stars evolve depends on their mass . You will draw a “flow chart” to represent the different stages of stellar evolution. Make sure to leave room between each stage (i.e. use the whole page) and be clear and neat in your chart. a. Using the terms at left, draw a flow chart for the evolution of a low-mass star. (You do not need to use all the terms here.) You should draw boxes connected with arrows so that the words in the boxes and the arrows between show the progressive evolution of a low-mass star (begin with Protostar and go from there) b. Now suppose the low-mass star had been born as part of a binary system. What other evolutionary steps need to be added to your chart? ( Circle these – instead of using boxes - so you know they represent evolutionary steps in a binary system only. ) c. Repeat (a) and (b) for a high-mass star. (You may need to re- use some terms and/or use new terms.) d. Are there any terms left over? If so, define them here: X-ray burster: An object that emits a burst of x-rays every few hours to every few days; each burst lasts a few seconds and is thought to be caused by helium fusion on the surface of an accreting neutron star in a binary system. Brown dwarf: An object that emits a burst of x-rays every few hours to every few days; each burst lasts a few seconds and is thought to be caused by helium fusion on the surface of an accreting neutron star in a binary system. Nova: An object that emits a burst of x-rays every few hours to every few days; each burst lasts a few seconds and is thought to be caused by helium fusion on the surface of an accreting neutron star in a binary system. Pulsar: A neutron star from which we observe rapid pulses of radiation as it rotates. 2. The terms in #1 are objects that represent stages of stellar evolution. Now let’s look at the terms that represent processes . a. Match the processes at left to the appropriate objects/stages in your flow charts. ( Use terms more than once, if needed. ) Are there any terms left over? If so, define them here: Neutrino Production: the process by which neutrinos are created by certain types of radioactive decay and nuclear reactions. Accretion: The process by which small objects come together to make larger objects. Supernova remnant Main-sequence star White dwarf Planetary nebula Neutron star X-ray binary Giant Brown dwarf Nova Supernova (massive star) X-ray burster Pulsar Protostar Supergiant Supernova (white dwarf) Hydrogen fusion CNO cycle Proton-proton chain Neutrino production Core-bounce Shell burning Degeneracy pressure Jets Accretion

ASTR 264 Lab 6 Degeneracy Pressure: A type of pressure unrelated to an object’s temperature, which arises when electrons or neutrons are packed so tightly that the exclusion and uncertainty principle come into play. Stellar Evolution Flow Charts 1 Low-mass Star Evolution Stellar Evolution Flow Charts 2 High-mass Star Evolution 1 These flow charts greatly simplify the stellar evolution process and leave out many important details. Still, I hope they will help you clarify and understand the information presented in class and in your book! 2 These flow charts greatly simplify the stellar evolution process and leave out many important details. Still, I hope they will help you clarify and understand the information presented in class and in your book!

ASTR 264 Lab 6 Part 1 – Black Holes 1. Log onto Mastering Astronomy and click on “Study Area”, then “Self-Guided Tutorials”. Do Lessons 1 and 2 of the “Black Holes” tutorial and answer the following questions. a. Explain what is meant by an object’s “escape velocity”. What is the Earth’s escape velocity?

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ASTR 264 Lab 6 The escape velocity is the minimum launch velocity at which the ball will move away from Earth forever. The escape velocity of Earth is about 11.2 km/s, which means that any object, such as a spacecraft or a rocket, must reach a speed of at least 11.2 km/s to escape Earth's gravitational pull and travel into space. b. What size would the Earth have to collapse to in order for its escape velocity to be close to the speed of light? 1 cm (1.0 × 10-51.0 times 10 to the power of -5 km) c. What would happen to the Hubble Space Telescope (currently orbiting Earth) if the Earth collapsed to a black hole? Explain . If the earth collapses into a black hole, it will cause catastrophe for the Hubble space telescope and all other satellites in earth orbit. It would be destroyed instantly. It would also mean a total loss of communication and control with any spacecraft in earth orbit and inability to collect and transmit database to earth-based telescopes. d. What is the event horizon of a black hole? Is there anything at the event horizon? The event horizon of a black hole is the boundary surrounding the black hole beyond which nothing, not even light, can escape its gravitational pull. Once an object crosses the event horizon, it is inside the black hole and cannot escape, with no physical material present. e. In an X-ray binary, what is the main reason the companion star’s outer layers feel a stronger gravitational pull from the black hole than from the star? The star's expansion pushes its outer layers far from its own center but closer to the black hole. The force of gravity at an object's surface decreases as radius increases. Thus, as the star swells, its hold on its outer gas weakens, while the same gas feels a stronger pull from the black hole. f. How do we determine if the accretion disk (emitting X-rays) is surrounding a black hole or a neutron star? To determine whether the accretion disk is surrounding a black hole or a neutron star, the following should be considered: mass measurement-ray emissions, time variability and gravitational waves Stop when you get to the part about supermassive black holes . 2. Let’s investigate further how we determine the mass of the compact object in an X-ray binary. For two objects of masses M 1 and M 2 that orbit each other, Newton’s theory of gravity gives the following relationship: M 1 + M 2 = 4 π 2 a 3 GP 2 , where P is the orbital period (in sec), a is the distance (in meters) between the objects, and G = 6.67 x 10 -11 (a constant). This equation is called Newton’s version of Kepler’s 3 rd Law.

ASTR 264 Lab 6 When we observe binary systems, we can often directly measure P (the period) and a (the distance between the objects). Thus, we can get an answer for the sum of the masses of the two objects. The mass of the companion star can be determined by plotting its position on an H-R diagram. Therefore, we can solve for the mass of the compact object. a. Cygnus X-1 was the first black-hole candidate detected. The compact object has an accretion disk that emits X-rays, and it orbits a supergiant star. The distance between the star and compact object is a = 3 x 10 10 m (0.2 AU) and they orbit each other with a period of P = 4.8 x 10 5 sec (5.6 days). Using this information, solve for the sum of the masses, M 1 + M 2 . (Your answer will be in kg.) M1 + M2 = 4π^2a^3/GP^2 M1 + M2 = 4π^(3 x 10^10 m)^3/(6.67 x 10^-11 m^3/kg.sec^2)(4.8x10^5 sec)^2 M1 + M2 ≈ 6.97 X 10^31 kg b. We know that the mass of the companion star is about M 1 = 5.4 x 10 31 kg (27 M Sun ). What is the mass of the compact object, M 2 ? M2 = (M1 – M2) – M1 M2 = (6.9 x 10^31 kg) – (5.4 X 10^31 kg) M2 ≈ 1.5 X 10^31 kg c. Neutron stars cannot be more than 3 M Sun . Convert the mass, M 2 , to solar masses (1 M Sun = 2 x 10 30 kg). Is the compact object a neutron star or black hole? M2 ≈ 1.5 X 10^31 kg X 1M sun/2X10^30 kg = 7.5Msum More precise calculations actually give a mass around 14-22 M Sun for Cygnus X-1.