How the first exoplanets were discovered – Astronomy Magazine

In 1992, astronomers discovered the first exoplanet, or planet outside our solar system. But it didnt come in any form theyd really anticipated.

Neutron stars are the second densest type of object in the universe outside black holes. They form when a giant star dies and explodes outward as a result of the collapse of its core. Put simply, the star becomes too massive to go on and expels all its energy into the surrounding space. The core is a sort of ground zero of this detonation. When that core collapses, depending on the size of the star, it becomes either a neutron star or a black hole.

Some neutron stars are called pulsars, for the regular pulses they give off in radio frequencies. Think of many of them like a drummer fast regular beats. Some pulsars, called millisecond pulsars, drum so fast that it would put Napalm Deaths drummer Danny Herrera to shame.

Those pulses are so regular that if they dont come at the right interval, astronomers know something is off.

A breakthrough in 1992 provided rock-solid evidence of planets. Astronomers Aleksander Wolszczan and Dale Frail tuned into the pulsar PSR B1257+12, 2300 light-years away. It should have pulsed every 0.006219 seconds, but every now and then, its pulses were a little off. Yet those off-beats came at regular intervals as well. After intensive study, Wolszczan and Frail came up with an explanation for why that was: it had two planets around it. One was three and the other four times the mass of Earth, and they rotated around every 67 and 98 days, rounded up.

Pulsar planets are somewhere in between a zombie and a chimera. When a star explodes, usually the planets in that system are destroyed or flung out by a shockwave. But after the violence settles down, the gas and dust can recondense. This, in effect, means that the three planets in B1257 may be made out of parts of the planets that came before them. Given the extreme radiation in these systems, almost no one has ever thought that the B1257 system could host life.

So, while the 1992 discovery was major news, it meant astronomers had the first verified planets around another star, but no proof of planets around a main sequence star like the Sun. That kind of confirmation was still a few years away.

Read More: 2019 Nobel Prize in Physics Awarded for Exoplanet Discovery

From the 1980s on, many groups had been on the hunt for the first planet around a Sun-like star. Some candidates came and went. Others required dozens or hundreds of observations to officially confirm.

But an observation in January 1995 proved to be the real deal. Didier Queloz, a grad student at the University of Geneva, was working with his advisor, Michel Mayor, on the search for extrasolar planets via radial velocity, in other words, wobbles.

Reportedly, his find was a chance coincidence. Out of a catalog of radial velocity signatures, he chose an F-type star called 51 Pegasi, roughly 50 light-years distant. He was trying to calibrate his planet finding code, opting for the star as one of a few promising candidates. It fell into place that night, a strong signal roughly every four days.

Measurements placed its minimum mass near Jupiter meaning the object was without a doubt a planet. While astronomers considered it possible to have such periods, it wasnt necessarily expected to find one in such a short period. At this time, I was the only one in the world who knew I had found a planet, Queloz told the BBC in 2016. I was really scared, I can tell you.

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How the first exoplanets were discovered - Astronomy Magazine