Most pow­er­ful grav­i­ta­tional waves event stands out among four new de­tec­tions

Tehran Times - - SCIENCE -

It’s been more than three years since as­tronomers first de­tected grav­i­ta­tional waves – rip­ples in the very fab­ric of space­time caused by some of the big­gest cat­a­clysms in the cos­mos. Now, an in­ter­na­tional team of sci­en­tists has pre­sented the full cat­a­log of these events, gath­ered over the last few years across two ob­ser­va­tion runs.

The cat­a­log con­tains a to­tal of 11 grav­i­ta­tional wave events, four of which are be­ing re­ported pub­licly for the first time. These events all be­gin as col­li­sions be­tween mas­sive cos­mic ob­jects – mostly black holes, but in one case a pair of neu­tron stars – which are pow­er­ful enough to send rip­ples of en­ergy spread­ing through the uni­verse.

By the time those rip­ples reach us here on Earth, though, the dis­tor­tions they cre­ate are mi­nus­cule, about a thou­sandth of the width of a pro­ton. By beam­ing lasers down long tun­nels and watch­ing for dis­tur­bances, fa­cil­i­ties like the Laser In­ter­fer­om­e­ter Grav­i­ta­tional-wave Ob­ser­va­tory (LIGO) in the U.S. and the Virgo grav­i­ta­tional-wave de­tec­tor in Europe are de­signed to de­tect even the tini­est rip­ples.

Be­tween black holes

The four newly-de­scribed ob­ser­va­tions all took place in July and Au­gust 2017, to­wards the end of LIGO’s sec­ond ob­serv­ing run. All four were the re­sult of col­li­sions be­tween black holes, and some of them marked new records.

An event known as GW170729 has taken two top hon­ors. De­tected on July 29, 2017, this event is both the most dis­tant and most mas­sive grav­i­ta­tional wave source found so far. These two black holes smashed to­gether 5 bil­lion light-years away – in other words, 5 bil­lion years ago – and re­leased en­ergy equiv­a­lent to the mass of five suns.

An­other new event, GW170818, was pin­pointed more pre­cisely than any other black hole merger. The two ob­jects crashed into each other about 2.5 bil­lion light-years from Earth, and the re­sult­ing waves were de­tected by both LIGO and Virgo, al­low­ing as­tronomers to iden­tify its po­si­tion in the sky to within 39 square de­grees. That pre­ci­sion is sec­ond only to the neu­tron star smashup de­tected just one day ear­lier, which was eas­ier to pin­point be­cause it was ac­com­pa­nied by light and ra­dio sig­nals.

The more grav­i­ta­tional wave events de­tected, the more we can learn about black holes, grav­ity, and the for­ma­tion of gal­ax­ies.

“We are learn­ing things about the pop­u­la­tion (of black holes), such as how fre­quently bi­nary black holes merge in the uni­verse (once ev­ery few hun­dred sec­onds some­where in the uni­verse) and whether small (low mass) or large (high mass) black holes are more com­mon – there are many more light black holes (around 5-10 times the mass of the sun) in the uni­verse than heavy black holes (around 30-40 times the mass of the Sun), but the heavy ones are ‘louder’ in grav­i­ta­tional-waves, and eas­ier to ‘hear’ col­lid­ing,” says Si­mon Steven­son, an au­thor on one of the stud­ies de­scrib­ing the work.

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