NASA stud­ies mys­te­ri­ous blast

Two teams ar­gue that it is ei­ther a black hole shred­ding a pass­ing star or it is a su­per­nova

DNA Sunday (Mumbai) - - SCITE H - —NASA

Abrief and un­usual flash spot­ted in the night sky on June 16, 2018, puz­zled as­tronomers and as­tro­physi­cists across the globe. The event — called AT2018­cow and nick­named “the Cow” after the co­in­ci­den­tal fi­nal let­ters in its of­fi­cial name — is un­like any ce­les­tial out­burst saw be­fore, prompt­ing mul­ti­ple the­o­ries about its source.

Over three days, the Cow pro­duced a sud­den ex­plo­sion of light at least 10 times brighter than a typ­i­cal su­per­nova, and then it faded over the next few months. This un­usual event oc­curred in­side or near a star-form­ing galaxy known as CGCG 137068, lo­cated about 200 mil­lion light-years away in the con­stel­la­tion Her­cules. The Cow was first ob­served by the NASA-funded As­teroid Ter­res­trial-im­pact Last Alert Sys­tem tele­scope in Hawaii.

So ex­actly what is the Cow? Us­ing data from mul­ti­ple NASA mis­sions, in­clud­ing the Neil Gehrels Swift Ob­ser­va­tory and the Nu­clear Spec­tro­scopic Tele­scope Ar­ray (NuSTAR), two groups are pub­lish­ing pa­pers that pro­vide pos­si­ble ex­pla­na­tions for the Cow’s ori­gins. One pa­per ar­gues that the Cow is a mon­ster black hole shred­ding a pass­ing star. The second pa­per hy­poth­e­sizes that it is a su­per­nova — a stellar ex­plo­sion — that gave birth to a black hole or a neu­tron star.

Re­searchers from both teams shared their in­ter­pre­ta­tions at a panel dis­cus­sion on Thurs­day, at the 233rd Amer­i­can Astro­nom­i­cal So­ci­ety meet­ing in Seat­tle.

„The zoomedin im­age shows the lo­ca­tion of the “Cow” in the galaxy

A Black Hole Shred­ding a Com­pact Star?

One po­ten­tial ex­pla­na­tion of the Cow is that a star has been ripped apart in what as­tronomers call a “tidal dis­rup­tion event.” Just as the Moon’s grav­ity causes Earth’s oceans to bulge, cre­at­ing tides, a black hole has a sim­i­lar but more pow­er­ful ef­fect on an ap­proach­ing star, ul­ti­mately break­ing it apart into a stream of gas. The tail of the gas stream is flung out of the sys­tem, but the lead­ing edge swings back around the black hole col­lides with it­self and cre­ates an el­lip­ti­cal cloud of ma­te­rial. Ac­cord­ing to one re­search team us­ing data span­ning from in­frared ra­di­a­tion to gamma rays from Swift and other ob­ser­va­to­ries.

Or a New View of a Su­per­nova?

If we’re see­ing the birth of a com­pact ob­ject in real time, this could be the start of a new chap­ter in our un­der­stand­ing of stellar evo­lu­tion Brian Grefen­stette, NuSTAR in­stru­ment sci­en­tist at Cal­tech

A dif­fer­ent team of sci­en­tists was able to gather data on the Cow over an even broader range of wave­lengths, span­ning from ra­dio waves to gamma rays. Based on those ob­ser­va­tions, the team sug­gests that a su­per­nova could be the source of the Cow. When a mas­sive star dies, it ex­plodes as a su­per­nova and leaves be­hind ei­ther a black hole or an in­cred­i­bly dense ob­ject called a neu­tron star. The Cow could rep­re­sent the birth of one of these stellar rem­nants.

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