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For a helpful analogy, contemplate our own Earth. Like a pulsar, it spins on an axis. Like a pulsar, it has a magnetic field. The magnetic field has an axis too, but it's different from the axis of rotation, that's why magnetic north is not the same as true north. There's no good reason for magnetic north to be the same as true north on a pulsar, either. And if it isn't, that magnetic axis whips round thirty times every second. A rapidly spi
If you're a living creature of remotely orthodox construction, you definitely do not want your star to be a pulsar. Synchrotron radiation is spread over a wide range of wavelengths, from visible light to x-rays, and x-rays can seriously damage the health of any creature of remotely orthodox construction. But no astronomer ever seriously suspected that pulsars might have planets, anyway. If a big star collapses down to an incredibly dense neutron star, surely it will gobble up all the odd bits of matter hanging around nearby. Won't it?
Perhaps not. In 1991 Matthew Bailes a
This technique first earned its keep with the discovery of double stars, where the dancing partner is a second star, and the wobbles are fairly pronounced because stars are far more massive than planets. As instrumentation has become more accurate, ever tinier wobbles can be detected, hence ever tinier dancing partners. Bailes a
Scarcely had this startling claim of a pulsar planet been withdrawn, however, when Aleksander Wolszczan and Dale Frail a
So there do exist planets outside our solar system. But it's the possibility of life that really makes distant planets interesting, and a pulsar planet with all those x-rays is definitely not a place for anything that wants to be alive for very long. But now conventional stars are turning out to have planets, too. In October 1995 Michel Mayor and Didier Queloz found wobbles in the motion of the star 51 Pegasi that were consistent with a planet of about half Jupiter's mass. Their observations were confirmed by Geoffrey Marcy and Paul Butler, who found evidence for two more planets, one seven times the mass of Jupiter orbiting 70 Virginis, and one two or three times Jupiter's mass orbiting 47 Ursae Majoris. By 1996 seven such planets had been found; right now there are about ten. The exact number fluctuates because every so often astronomers discover problems with previous measurements that cast doubt on somebody else's favourite new planet, but the general trend is up. And our nearest sunlike neighbour, epsilon Eridani, is now known to possess an encircling dustcloud, perhaps like our Sun's Oort cloud, thanks to observations made in 1998 by James Greaves and colleagues. We can't see any wobbles, though, so if it has planets, their mass must be less than three times that of Jupiter. A year earlier, David Trilling and Robert Brown used observations of a similar dustcloud round 55 Cancri, which does wobble, to show that it has a planet whose mass is at most 1.9 Jupiters. This definitely rules out alternative explanations of the unseen companion, for example that it might be a 'brown dwarf', a failed star.
Although today's telescopes ca
But you don't have to use just one telescope.
A technique known as 'interferometry' makes it possible, in principle, to replace a single mirror 100 yards wide by two much smaller mirrors 100 yards apart. Both produce images of the same star or planet, and the incoming light waves that form those images are aligned very accurately and combined. The two-mirror system gathers less light than a complete 100-yard mirror would, but it can resolve the same amount of tiny detail. And with modern electronics, very small quantities of incoming light can be amplified. In any case, what you actually do is use dozens of smaller mirrors, together with a lot of clever trickery that keeps them aligned with each other and combines the images that they receive in an effective ma
Radio astronomers use this technique all the time. The biggest technical problem is keeping the length of the path from the star to its image the same for all of the smaller telescopes, to within an accuracy of one wavelength. The technique is relatively new in optical astronomy, because the wavelength of visible light is far shorter than that of radio waves, but for visible light the real killer is that it's not worth bothering if your telescopes are on the ground. The Earth's atmosphere is in continual turbulent motion, bending incoming light in unpredictable ways. Even a very powerful ground-based telescope will produce a fuzzy image, which is why the Hubble Space Telescope is in orbit round the Earth. Its pla