Through the Past, Credit: Edo Berger, Harvard University. Harvard University. Credit: Edo Berger, Brightly Gamma-Ray Bursts and the Early Universe By Sarah Harland-Logan Midnight Messages one GRB is equivalent to the energy ust like many undergraduates, Pro- output of 1,000 stars the size of the Jfessor Edo Berger (of the Harvard Sun, throughout their entire lives (3). astronomy department) is used to These incredibly intense bursts of receiving the occasional late-night gamma radiation (the highest-energy text message. Berger’s midnight texts, portion of the light spectrum) are now however, are sent to his iPhone directly believed to occur somewhere in the from NASA’s Swift telescope, our universe at least once to a few times per “The astronomy most powerful tool for detecting the day, and perhaps far more frequently phenomena known as Gamma-Ray (3, 6). Berger typically receives about equivalent of Bursts (GRBs) (1). Berger holds the two texts per week informing him of working at the ER” record for discovering the most dis- the appearance of a new one. At this tant, and therefore the oldest, object point, he will “Jump out of bed and in the known universe; this object is start calling observatories around the somewhat disappointingly named world to observe the burst,” and then GRB 090423 (to indicate that it was begin analyzing its properties as soon discovered on April 23, 2009) (2, 3). as possible (1). GRBs are the brightest objects in the Some of us might resent this frequent known universe, and the most power- incursion upon our sleep patterns, but ful explosions since the Big Bang (4, Berger explains that the unpredictable 5). For the brief period that a GRB is and “fast-paced nature” of his work is occurring, it shines thousands of times “part of the fun.” He describes his job more brightly than the entire galaxy in as “the astronomy equivalent of work- which it resides (1). In fact, GRBs are ing at the ER,” and is happy both to so bright that the energy released by be free from the type of work “where fall 2010 Harvard Science Review 9 GRBs went unnoticed until mid- ing it, and autonomously reorients itself 1969, when physicist Ray Klebasabel in the direction of the burst, where it was working with the data produced observes the burst’s afterglow. Perhaps by Vela, and noticed an earlier burst unsurprisingly, both types of GRBs are of gamma radiation that had to be now believed to result from the forma- extraterrestrial in origin (6, 7, 8). His tion of black holes, everyone’s favorite GLVFRYHU\FDWDO\]HGDÀHUFHGHEDWHRQ space monsters (4, 9). the origin and nature of GRBs that would continue for decades (1). Like Black Holes and Revelations any good scientific mystery, GRBs GRBs are subdivided into two cat- soon attracted a spectacular array of egories, “long” and “short.” Long theories, which ran the gamut from the GRBs, which can last for hundreds of reasonable-sounding (e.g., GRBs were seconds, begin life with the supernova caused by collisions between comets of a star at least 20 to 30 times (and Credit: Edo Berger (Harvard). and neutron stars) to the hilariously perhaps even 100 times) more massive outlandish (e.g., they were produced than the Sun (1). When giant stars like Figure 1. The record-breaking GRB (090423). not by Soviet nuclear testing but rather these explode, a black hole is created at by alien nuclear warfare) (6, 8). A 1975 the center of the supernova, and matter people . plan things months in ad- review paper presented at the Texas from the exploded star then forms an vance,” and that he and his colleagues Symposium on Relativistic Astrophys- accretion disc around the black hole. actually get “to look at pretty pictures ics included literally 100 different GRB As this taurus of material is sucked of the universe in real time” (also unlike theories (6). into the black hole, some of the mat- many astrophysicists) (1). 7RGD\WKHUHPDUNDEOH*5%ÀQGLQJ ter is ejected (along with electromag- satellite Swift (named for the bird) en- netic radiation), at velocities as high as Star Wars? ables scientists to make rapid progress 99.9995% of the speed of light (10); the +XPDQVÀUVWHQFRXQWHUHG*DPPD toward GRBs’ true origin. Swift has precise details of this process are still Ray Bursts by unknown to accident, dur- cosmolo- ing a military gists (11). o p e r a t i o n . The matter T h e f i r s t is thrown GRB detec- o u t w a r d tion occurred in several on July 2, d i f f e r e n t 1967, thanks “ s h e l l s , ” to a U.S. De- each travel- p a r t m e n t ing at a dif- of Defense ferent speed program that (3). GRBs launched the occur when Vela satellite more rap- system, in or- idly mov- der to moni- ing “shells” Credit: Lynn Cominski, Sonoma. Credit: Lynn tor Soviet catch up compliance to slower with the Nu- Figure 2. Accumulated GRB map, highlighting the most recent burst at any given moment (April 15, 2010). shells and clear Test Ban Credit: Lynn Cominski, Sonoma. c o l l i d e Treaty. The with them, 9HODVDWHOOLWHVZHUHÀWWHGZLWKHTXLS- LGHQWLÀHGDSSUR[LPDWHO\*5%VSHU releasing very high-energy photons; ment that could detect gamma-rays, so year since its launch on November 20th, hundreds of these collisions are pos- as to identify the radiation signature of 2004 (4). It alerts astrophysicists like sible in a single GRB (3, 11, 12). any Soviet warheads illegally detonated Dr. Berger to the location of each new But although astrophysicists are in space (6, 7, 8). GRB within about 1 minute of detect- FRQÀGHQWWKDWORQJ*5%VDUHLQGHHG 10 Harvard Science Review fall 2010 ORFDOL]HWKHPZLWKVXIÀFLHQWSUHFLVLRQ to identify their host galaxies, quantify how much energy they release, and GHÀQLWLYHO\DVVRFLDWHORQJ*5%VZLWK supernovae (15, 16, 17). Without the afterglows, we would still be groping around in the dark. Illuminating the Cosmic Dark Age Not only are GRBs interesting phe- nomena in themselves, but Dr. Berger and his colleagues hope to use them as ´WKHEHVWÁDVKOLJKWµWRLOOXPLQDWHWKH early history of the universe (1). Dr. Berger reminded me that “When we look at the universe, we’re looking at light travelling from distant objects. Figure 3. GRB 090423 shatters distance records. Brilliant Afterglows *LYHQWKDWWKHVSHHGRI OLJKWLVÀQLWHµ We owe the preponderance of our the more distant the object we are produced from these supernovae, current GRB knowledge to the 1997 looking at, “the further back in time Berger emphasized that their origin detection (by the BeppoSAX satellite) we’re looking.” In other words, “the story is not yet complete, because “we of the “afterglows” that they leave key” to answering questions like “How only have one GRB for every 1,000 behind; we are currently able to detect GLGWKHÀUVWVWDUVIRUP"µLVWR´ORRNDW supernova explosions. We must need about two-thirds of them (15, 16, 17). extremely distant objects, [from] when something very special to happen [to Once the collisions of the ejected shells the universe was young” (1). produce a GRB]; we just don’t know of matter have ceased (and therefore Between the beginning of time and what it is. Yet.” (1) the GRB is over), the large shell that has the present day, the universe passed The story of short GRBs, which resulted from these collisions continues through a period of literal darkness can be as brief as a few milliseconds, to travel outward at nearly the speed of that is referred to as the Cosmic Dark remains enmeshed in even greater mys- light, colliding with the interstellar me- Age. In the aftermath of the Big Bang, tery. The current theory (which Berger dium; Dr. Berger compares its advance the universe was incredibly hot, and its emphasizes is “something that we’re to “a snowplow pushing snow.” (18) matter was entirely ionized (1, 9); the [still] trying to prove or disprove at this formation of atoms did not occur for point”) is that they are produced when about 400,000 years (1). This process a pair of neutron stars nearly collide, Dr. Berger’s record-holding GRB has a redshift of 8.2, which created the Cosmic Microwave Back- after the stars lose the angular momen- ground (CMB), the low-level micro- tum that keeps their orbit stable (1, 6). means that this GRB occurred wave radiation that glows evenly at As Berger colorfully puts it, “eventually about 630 million years after all points throughout the cosmos (5). they get so close to each other that the Big Bang; the light from During this period, the universe they’re almost touching; then they start was plunged into darkness, since vis- shredding each other. At the end, this burst has been traveling for over 13 of the universe’s ible light was absorbed by clouds of they don’t actually collide; but they hydrogen gas. Since ionized matter just tear each other apart, in those last 13.7 billion years of existence. DOORZVSKRWRQVWRÁRZIUHHO\ZKHUHDV few seconds.” (1) A black hole forms atomic gas absorbs them (18), the uni- at the site of the shredded remnant; it This collision generates emissions in the YHUVHUHPDLQHGGDUNXQWLOWKHÀUVWVWDUV is surrounded by an accretion disc of lower portions of the spectrum (X-rays, had been formed. Photons emitted by matter from the neutron stars, which is optical, and microwaves), which linger the early stars and galaxies then “re- sucked into the black hole; and again, for a period ranging from days to years ionized” the matter of the intergalactic this process drives the incredibly rapid (1, 12).