`We can now track the birth, evo­lu­tion and death of stars'

Down to Earth - - SPECIAL REPORT -

In some ways, the de­tec­tion of grav­i­ta­tional waves (GWs) con­firms the way the uni­verse op­er­ates. In par­tic­u­lar, it con­firms a long-stand­ing pre­dic­tion of gen­eral rel­a­tiv­ity, adding to the ear­lier ex­per­i­men­tal con­fir­ma­tions. We also ex­pected GWs to be real based on the ob­ser­va­tions of as­tronomers who have tracked the changes in bi­nary pul­sar or­bits. But it is won­der­ful to be able to de­tect the waves di­rectly! The fact that we de­tected two heavy black holes merg­ing as our first sig­nal is in­ter­est­ing. Some peo­ple ex­pected that to be a com­mon source, while oth­ers did not, based on dif­fer­ent astro­phys­i­cal mod­el­ing. So this event is al­ready telling us some­thing about how stars form and evolve to pro­duce heavy bi­nary black hole sys­tems.

It was very hard to de­tect the waves. We had in­di­rect proof be­fore, but this is the first di­rect proof of their ex­is­tence. Since events like bi­nary merg­ers are rare, we have to be able to search a large vol­ume of the uni­verse, and the ones we de­tect tend to be rather far away. The grav­i­ta­tional-wave strain is very tiny when it reaches Earth. That's why it took many years of re­search to ar­rive at de­tec­tors which are sen­si­tive enough.

This dis­cov­ery is one more con­fir­ma­tion of our un­der­stand­ing of mass and grav­ity through gen­eral rel­a­tiv­ity, but this mea­sure­ment does not say any­thing about other in­ter­ac­tions of mat­ter.

In the fu­ture, we will be able to de­tect things that aren't seen in other ways. Merg­ers of bi­nary black holes and bi­nary neu­tron stars, for in­stance. We'll also learn about the pop­u­la­tion and prop­er­ties of those things in our uni­verse. That will give us more in­for­ma­tion to test mod­els of birth, evo­lu­tion and deaths of stars and their galac­tic en­vi­ron­ments. PETER S SHAWHAN As­so­ciate pro­fes­sor of physics, Univer­sity of Mary­land, USA. He is closely as­so­ci­ated with the LIGO pro­ject

(As told to Down­ToEarth)

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