Understanding the Scale of Earth vs. Neutron Stars

Why do astronomers think the star system Cygnus X-1 contains a black hole? It emits X-rays characteristic of an accretion disk, and the unseen object in the system is too massive to be a neutron star. What is the ultimate fate of an isolated white dwarf? It will cool down and become a cold black dwarf. Sirius, the brightest star in the night sky, is actually a binary star system. Sirius A is main-sequence star and Sirius B is a white dwarf. Nearly all the visible light we see from Sirius comes from Sirius A. But when we photograph the system with X-ray light, as shown here, Sirius B is the brighter of the two stars. Why? As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more X rays. What is this a picture of? It is a painting of close binary star system in which the star on the right is a white dwarf surrounded by an accretion disk filled with gas drawn by gravity from the companion star on the left. Based on the curves shown here, which of the following statements best describes how we can distinguish a massive star supernova from a white dwarf supernova? A white dwarf supernova is brighter at its peak and over a few months fades more steadily than a massive star supernova. Which of the following diagrams best represents the scale of Earth in comparison to a neutron star? Earth big. neutron star tiny. Which of the following represents the true shape of a black hole as you'd see it (or measure it) as you flew past it in a spaceship? sphere A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft's orbit will be affected? curve with dot not touching This series of images shows the pulsar at the center of the Crab Nebula looking bright every 0.033 second. Based on these data and current theory of pulsars, what can we conclude? The pulsar is a neutron star that makes one full rotation every 0.033 second This painting shows an accretion disk around a black hole in a close binary star system. What physical law explains why matter flowing from the companion star orbits rapidly as it nears the black hole? The law of conservation of angular momentum A binary system that looks like the one shown in this painting should shine brightly in X rays. Which one of the four labeled regions is the source of most of the X rays? II This graph shows data collected by a gamma ray telescope. What kind of event is it showing? a gamma ray burst from a distant galaxy This graph shows about 20 seconds of data from a pulsar. Based on current understanding of pulsars, what can we conclude? The pulsar is a neutron star that makes one full rotation about every 1.34 seconds. This graph shows a gravitational wave signal recorded by the gravitational wave detectors (called LIGO) in two locations? What do models indicate was the cause of this signal? The merger of two black holes in a distant galaxy. Based on current evidence, which of the following statements about gamma ray bursts is true? All those that we have detected occurred in distant galaxies 3 At peak brightness, the white dwarf supernova is approximately __________ times as luminous as the massive star supernova at its peak brightness. 1% For the white dwarf supernova, the luminosity 175 days after it reaches peak brightness is about __________ of the luminosity at peak brightness. 30 days Approximately how many days does it take for a white dwarf supernova to decline to 10% of its peak brightness? 100 days Approximately how many days does it take for a massive star supernova to decline to 10% of its peak brightness? 300 days Approximately how many days does it take for a massive star supernova to decline to 1% of its peak brightness? If you were to come back to our Solar System in 6 billion years, what might you expect to find? a white dwarf What is the ultimate fate of an isolated pulsar? It will spin ever slower, the magnetic field will weaken, and it will cease to be a pulsar. A typical white dwarf is _________. as massive as the Sun but only about as large in size as Earth Why is there an upper limit to the mass of a white dwarf? The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported. Imagine comparing a 1.2 solar mass white dwarf to a 1.0 solar mass white dwarf. Which of the following must be true? The 1.2 solar mass white dwarf has a smaller radius. According to our modern understanding, what is a nova? an explosion on the surface of a white dwarf in a close binary system. A typical neutron star is more massive than our Sun and about the size (radius) of _________. a small asteroid (10 km in diameter) What caused the rapid spin of a neutron star that we see as a pulsar? the conservation of angular momentum during the collapse of the original star's core A neutron star is ________. the core remnant of a star that died in a massive star supernova What do we mean by the event horizon of a black hole? It is the point beyond which neither light nor anything else can escape. How does a black hole form from a massive star? During a supernova, if the mass of the infalling core has enough gravity to overcome neutron degeneracy pressure, the core will collapse to a black hole. Which of the statements below about black holes is not true? A spaceship passing a few million kilometers from a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass mainsequence star. The maximum mass of a white dwarf is _________. about 1.4 times the mass of our Sun Pulsars are thought to be _________. rapidly rotating neutron stars The more massive a white dwarf, the ________. smaller its radius From an observational standpoint, what is a pulsar? an object that emits flashes of light several times per second (or even faster), with near perfect regularity The Schwarzschild radius of a black hole depends on ________. only the mass of the black hole Which of the following statements about novae is not true? Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now A typical white dwarf is ________. as massive as the Sun but only about as large in size as Earth