Figure 9.25: Artist’s illustration of an ‘isolated neutron star’ – one without radio pulsations or binary companions. Most detected neutron stars, however, are pulsars, and emit radio radiation. The existence of neutron stars was first proposed by Walter Baade and Fritz Zwicky in 1934, when they argued that a small, dense star consisting primarily of neutrons would be the living result of a star of size somewhat larger than the sun dying in a supernova explosion. The rotation energy of the mother star is preserved in the neutron star so they spin rapidly, at between 1,000 times a second and once every few seconds. The mother star’s magnetic field is also condensed in the neutron star. Electrons and protons given off from the surface of the neutron star are caught up in the intense magnetic field and spun around to emit radio waves in narrow beams at the magnetic poles.


A star ten times the mass of the sun uses fuel 5,000


times faster since the star’s core has raised temperature and pressure due to higher gravity. Such a massive star uses up hydrogen in its core in a few million years and becomes a red supergiant, which continues nuclear reactions using higher elements. Eventually, when the nuclear reactions cease, the core collapses, and the star blows apart into a supernova. It leaves behind a tiny, extremely dense object called a neutron star. The time from birth to death of this massive star is only 20 million years. Te largest stars, with 30 sun masses or more, live fast and


die young. Teir cores are so massive that they leave behind a black hole.


9.1.8 What Will Happen to Our Earth?


Our sun formed roughly 4.6 billion years ago. Our Earth began its life 40 million years afterwards. We have seen that it is nuclear fusion in the sun’s core that makes it emit energy and light, providing conditions for life and growth. Fusion will last for another 5.4 billion years, but the sun will go through some serious changes before its death. Te sun has been increasing its brightness by about 10%


every billion years it spends burning hydrogen. Tis increase in luminosity also means significant increase in the heat energy our planet receives. Over the next 1 billion years, this will trigger a runaway greenhouse effect similar to that which turned Venus into the hottest planet in the solar system. Bright light from the sun strikes the ground of the Earth, and warms it up. Te ground tries to radiate heat back into space but carbon


Figure 9.26: In 1967, post-graduate student Jocelyn Bell found a strange signal while making a radio sweep of the sky. It pulsed regularly every 1¹⁄3 seconds. It was not signals from aliens, and was identified as a pulsar – a rotating neutron star that emits a beam of electromagnetic radiation, which can only be seen when the beam of emission is pointing toward Earth. The timing of the pulses can be measured with extraordinary accuracy by radio telescopes. A binary pulsar is a pulsar with a binary companion, often a white dwarf or neutron star. The first binary pulsar was discovered in 1974 by Russell Hulse and Joseph Taylor, for which they won the 1993 Nobel Prize in Physics (see Section 9.4.1). Einstein’s theory of general relativity predicts that two neutron stars would emit gravitational waves as they orbit a common centre of mass, which would carry away orbital energy and cause the two stars to draw closer together and shorten their orbital period. Prior to 2015 and the operation of LIGO (see Section 9.4), binary pulsars were the only tools physicists had to infer evidence of gravitational waves.


dioxide traps much of it around the planet, heating it up. At some point, all the water on the Earth’s surface will evaporate into the atmosphere. Water vapour is an even more powerful greenhouse gas than carbon dioxide and this will cause temperatures to rise even more. Approximately 3.5 billion years from now, the sun will be


40% brighter than it is today. What is left of our oceans will boil. Te ice caps will melt. All water vapour in the atmosphere will be lost to space. Earth will become a hot, dry world, just like Venus is today. In 5.4 billion years from now, the sun will enter into the red


giant phase of its evolution. Te core heats up and gets denser, causing the sun to grow in size. Te expanding red sun will consume Mercury, Venus and Earth (Schroder and Smith, 2008). Once inside the sun’s atmosphere, the Earth will spiral inward in a fiery death. Without any more fuel to burn, the sun will expel its outer layers and then collapse into a white dwarf, which then slowly cools down over trillions of years. Te good news, if any, in this somewhat speculative story


is that much of the outer solar system in 1–2 billon years will be in the sun’s habitable zone. In the Kuiper Belt formerly icy worlds will melt, and liquid water will be present beyond the orbit of Pluto. Pluto will be the new Venus. Perhaps Eris will be our new home? If man is still around 1–2 billion years from now, he may want to consider getting out of the way so that he can live happily till the sun reaches the end of its life. Tat is all presuming a cataclysmic event does not hit us


soon; in the meantime, let’s hope that we have plenty of days of sunshine to look forward to!


309


Casey Reed/Penn State University


Michael Kramer (Jodrell Bank Observatory, University of Manchester)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228  |  Page 229  |  Page 230  |  Page 231  |  Page 232  |  Page 233  |  Page 234  |  Page 235  |  Page 236  |  Page 237  |  Page 238  |  Page 239  |  Page 240  |  Page 241  |  Page 242  |  Page 243  |  Page 244  |  Page 245  |  Page 246  |  Page 247  |  Page 248  |  Page 249  |  Page 250  |  Page 251  |  Page 252  |  Page 253  |  Page 254  |  Page 255  |  Page 256  |  Page 257  |  Page 258  |  Page 259  |  Page 260  |  Page 261  |  Page 262  |  Page 263  |  Page 264  |  Page 265  |  Page 266  |  Page 267  |  Page 268  |  Page 269  |  Page 270  |  Page 271  |  Page 272  |  Page 273  |  Page 274  |  Page 275  |  Page 276  |  Page 277  |  Page 278  |  Page 279  |  Page 280  |  Page 281  |  Page 282  |  Page 283  |  Page 284  |  Page 285  |  Page 286  |  Page 287  |  Page 288  |  Page 289  |  Page 290  |  Page 291  |  Page 292  |  Page 293  |  Page 294  |  Page 295  |  Page 296  |  Page 297  |  Page 298  |  Page 299  |  Page 300  |  Page 301  |  Page 302  |  Page 303  |  Page 304  |  Page 305  |  Page 306  |  Page 307  |  Page 308  |  Page 309  |  Page 310  |  Page 311  |  Page 312  |  Page 313  |  Page 314  |  Page 315  |  Page 316  |  Page 317  |  Page 318  |  Page 319  |  Page 320  |  Page 321  |  Page 322  |  Page 323  |  Page 324  |  Page 325  |  Page 326  |  Page 327  |  Page 328  |  Page 329  |  Page 330  |  Page 331  |  Page 332  |  Page 333  |  Page 334  |  Page 335  |  Page 336  |  Page 337  |  Page 338  |  Page 339  |  Page 340  |  Page 341  |  Page 342  |  Page 343  |  Page 344  |  Page 345  |  Page 346  |  Page 347  |  Page 348  |  Page 349  |  Page 350  |  Page 351  |  Page 352