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Blast called furthest object visible to naked eye

March 20, 2008
Courtesy NASA
and World Science staff

A gi­gantic stel­lar ex­plo­sion de­tected March 19 by has shat­tered the rec­ord for the fur­thest ob­ject vis­i­ble with the na­ked eye, sci­en­tists say—half­way across the known uni­verse.

Sad­ly, the show lasted only hours. But “if some­one just hap­pened to be look­ing at the right place at the right time, they saw the most dis­tant ob­ject ev­er seen by hu­man eyes with­out op­ti­cal aid” on record, said Ste­phen Hol­land of NASA’s God­dard Space Flight Cen­ter in Green­belt, Md.

The af­ter­glow of GRB 080319B was im­aged by Swift's X-ray Tel­e­scope (left) and Op­ti­cal/Ul­tra&s Tel­e­scope (right). (Cred­it: NA­SA/Swift/Ste­fan Imm­ler, et al.)


De­tected by the agen­cy’s Swift sat­el­lite, the ex­plo­sion was a gam­ma ray burst, a type of blast that usu­ally oc­curs when mas­sive stars run out of their nu­clear fu­el. Their cores col­lapse to form ex­tremely dense ob­jects known as black holes or neu­tron stars. In the pro­cess they re­lease a great burst of high-en­er­gy gam­ma rays and par­t­i­cle jets that rip through space at nearly light speed.

As the jets plow in­to sur­round­ing interstel­lar clouds, they heat the gas, of­ten gen­er­at­ing bright af­ter­glows. Gam­ma ray bursts are be­lieved to be the most lu­mi­nous ex­plo­sions in the uni­ver­se, and this one “was a whop­per,” said Swift prin­ci­pal in­ves­ti­ga­tor Neil Gehrels of the God­dard cen­ter. “It blows away ev­ery gam­ma ray burst we’ve seen so far.”

Swift’s Burst Alert Tel­e­scope pick­ed up the burst at 2:12 a.m. Eastern U.S. time and pin­pointed the co­or­di­nates in the con­stella­t­ion Boötes, re­search­ers said. Tel­e­scopes in space and on the ground quickly moved to catch the af­ter­glow. The burst is named GRB 080319B, be­cause it was the sec­ond gam­ma ray burst found that day.

Two oth­er Swift in­stru­ments al­so ob­served af­ter­glows. Sev­eral ground-based tele­scopes saw the af­ter­glow bright­en to vis­u­al mag­ni­tudes be­tween 5 and 6, in the scale used by as­tro­no­mers. The brighter an ob­ject is, the low­er its mag­ni­tude num­ber. From a dark loca­t­ion in the coun­try­side, peo­ple with nor­mal vi­sion can see stars slightly faint­er than mag­ni­tude 6. 

Thus the af­ter­glow would have been dim, but vis­i­ble to the na­ked eye, said Hol­land, a mem­ber of the Swift sci­ence team.

Lat­er, the Very Large Tel­e­scope in Chil­e and the Hobby-Eberly Tel­e­scope in Tex­as meas­ured the burst’s red­shift at 0.94. A red­shift is a meas­ure of the dis­tance to an ob­ject. A red­shift of 0.94 trans­lates in­to a dis­tance of 7.5 bil­lion light years, mean­ing the ex­plo­sion took place 7.5 bil­lion years ago, a time when the uni­ver­se was less than half its cur­rent age and Earth had yet to form. The burst was seen oc­cur­ring in the dis­tant past because its light takes so long to reach us.

“No oth­er known ob­ject or type of ex­plo­sion could be seen by the na­ked eye at such an im­mense dis­tance,” said Hol­land. 

GRB 080319B’s op­ti­cal af­ter­glow was 2.5 mil­lion times more lu­mi­nous than the most lu­mi­nous su­per­no­va, or stel­lar ex­plo­sion, ev­er rec­orded, sci­en­tists said. That would make it the most in­trin­sic­ally bright ob­ject ev­er ob­served by hu­mans. The most dis­tant pre­vi­ous ob­ject that could have been seen by the na­ked eye is the near­by gal­axy M33, a rel­a­tively short 2.9 mil­lion light-years from Earth. 

Anal­y­sis of GRB 080319B is just get­ting un­der­way, so as­tro­no­mers don’t know why this burst and its af­ter­glow were so bright. One pos­si­bil­ity is the burst was more en­er­get­ic than oth­ers, per­haps be­cause of the mass, spin, or mag­net­ic field of the pro­gen­i­tor star or its jet, sci­ent­ists said. Or per­haps it con­cen­trat­ed its en­er­gy in a nar­row jet aimed di­rectly at Earth.

GRB 080319B was one of four bursts that Swift de­tected, a Swift rec­ord for one day—as it hap­pened, the same day ac­claimed sci­ence-fiction writ­er Ar­thur C. Clarke died. “Co­in­ci­den­tally, [his death] seems to have set the uni­ver­se ablaze with gam­ma ray bursts,” said Swift sci­ence team mem­ber Ju­dith Ra­cu­sin of Penn State Uni­ver­s­ity.


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A gigantic stellar explosion detected March 19 by has shattered the record for the furthest object visible with the naked eye, scientists say—halfway across the universe. Sadly, the show lasted only hours. But “if someone just happened to be looking at the right place at the right time, they saw the most distant object ever seen by human eyes without optical aid,” said Stephen Holland of NASA’s Goddard Space Flight Center in Greenbelt, Md. Detected by the agency’s Swift satellite, the explosion was a gamma ray burst, a type of blast that usually occurs when massive stars run out of their nuclear fuel. Their cores collapse to form extremely dense objects known as black holes or neutron stars. In the process they release a great burst of high-energy gamma rays and particle jets that rip through space at nearly light speed. As the jets plow into surrounding interstellar clouds, they heat the gas, often generating bright afterglows. Gamma ray bursts are believed to be the most luminous explosions in the universe, and this one “was a whopper,” said Swift principal investigator Neil Gehrels of NASA’s Goddard Space Flight Center in Greenbelt, Md. “It blows away every gamma ray burst we’ve seen so far.” Swift’s Burst Alert Telescope picked up the burst at 2:12 a.m. EDT, March 19, and pinpointed the coordinates in the constellation Boötes, researchers said. Telescopes in space and on the ground quickly moved to catch the afterglow. The burst is named GRB 080319B, because it was the second gamma ray burst found that day. Two other Swift instruments also observed afterglows. Several ground-based telescopes saw the afterglow brighten to visual magnitudes between 5 and 6, in the scale used by astronomers. The brighter an object is, the lower its magnitude number. From a dark location in the countryside, people with normal vision can see stars slightly fainter than magnitude 6. Thus the afterglow would have been dim, but visible to the naked eye, said Holland, a member of the Swift science team. Later, the Very Large Telescope in Chile and the Hobby-Eberly Telescope in Texas measured the burst’s redshift at 0.94. A redshift is a measure of the distance to an object. A redshift of 0.94 translates into a distance of 7.5 billion light years, meaning the explosion took place 7.5 billion years ago, a time when the universe was less than half its current age and Earth had yet to form. This is more than halfway across the visible universe. “No other known object or type of explosion could be seen by the naked eye at such an immense distance,” said Holland. GRB 080319B’s optical afterglow was 2.5 million times more luminous than the most luminous supernova, or stellar explosion, ever recorded, scientists said. That would make it the most intrinsically bright object ever observed by humans. The most distant previous object that could have been seen by the naked eye is the nearby galaxy M33, a relatively short 2.9 million light-years from Earth. Analysis of GRB 080319B is just getting underway, so astronomers don’t know why this burst and its afterglow were so bright. One possibility is the burst was more energetic than others, perhaps because of the mass, spin, or magnetic field of the progenitor star or its jet. Or perhaps it concentrated its energy in a narrow jet that was aimed directly at Earth. GRB 080319B was one of four bursts that Swift detected, a Swift record for one day—as it happened, the same day as acclaimed science-fiction writer Arthur C. Clarke died. “Coincidentally, [his death] seems to have set the universe ablaze with gamma ray bursts,” said Swift science team member Judith Racusin of Penn State University.