This research news article discusses two studies that propose different models to explain an unusual gamma-ray burst (GRB) called the "Christmas burst" that occurred on Christmas Day in 2010. One study suggests the GRB originated from a tightly bound binary system of a neutron star and supergiant helium star that merged, producing a jet within a common gas envelope. The other study proposes that a minor body like an asteroid or comet was tidally disrupted after passing close to a neutron star, producing debris that formed a disk and caused multiple emission peaks. While both models can explain aspects of the complex data from the unusual GRB, the article notes that at least one model must be incorrect as the definitive proof

1. NEWS & VIEWS RESEARCH
manipulated to create a range of models from Andrew J. Whittle and Antonio Vidal-Puig
those for Alzheimer’s disease to HIV infec- are in the Department of Clinical
tion. Therefore, any published study that is Biochemistry, University of Cambridge
based on the manipulation of macrophages Metabolic Research Laboratories,
may need to be re-examined, because sci- Institute of Metabolic Science, NIHR
entists should ask whether the effects they Cambridge Biomedical Research Centre,
observed were the result of direct manipu- Addenbrooke’s Hospital, Cambridge
lation of the immune system or a result of CB2 0QQ, UK.
secondary alterations in the activity of the e-mails: ajw232@medschl.cam.ac.uk;
central nervous system. ajv22@cam.ac.uk
Addressing whether such genetic manipu-
1. Cypess, A. M. et al. N. Engl. J. Med. 360, 1509–1517
lations alter how the mouse brain ‘perceives’ (2009).
its environment is beyond the scope of the 2. Ouellet, V. et al. J. Clin. Endocrinol. Metab. 96,
present work. Furthermore, Nguyen et al. do 192–199 (2011).
3. Saito, M. et al. Diabetes 58, 1526–1531 (2009).
not explore the proportional contribution of 4. Cannon, B. & Nedergaard, J. Physiol. Rev. 84,
macrophages to nervous-system activity. What 277–359 (2004).
they do show, however, is that alternatively 5. Nguyen, K. D. et al. Nature 480, 104–108 (2011).
6. Gandotra, S. et al. J. Biol. Chem. 286, 34998–35006
activated macrophages are key to how the (2011).
body handles and burns its fat stores. In that 7. Huang-Doran, I. et al. J. Endocrinol. 207, 245–255
respect, this specialized, widely distributed (2010).
group of cells could represent a novel target 8. Flierl, M. A. et al. Nature 449, 721–725 (2007).
9. Weisberg, S. P. et al. J. Clin. Invest. 112, 1796–1808
for therapies for obesity and other fat-storage (2003).
disorders. ■ 10. Prieur, X. et al. Diabetes 60, 797–809 (2011).
AST RO PHYSICS
A puzzling γ-ray burst
The population of γ-ray bursts is sometimes enriched by perplexing events
that challenge established theoretical models. Two teams get to grips with
understanding one such event — the ‘Christmas’ burst. See Letters p & p
.69 .72
E N R I C O C O S TA to point towards an observer, a bright emis-
G
sion — the prompt γ-ray release — is detected.
amma-ray bursts strike Earth’s The GRB afterglow, which follows minutes
atmosphere from random directions after the initial burst and fades away over the
in space about twice a day. In 1997, the course of weeks or months, is emitted at vari-
discovery1 of the emission, or afterglow, that ous wavelengths and is caused by the impact of
follows the prompt release of γ-rays placed their the jet on the surrounding interstellar medium.
progenitors in remote galaxies. The mecha- Once the GRB fades away, the faint galaxy that
nisms put forward to explain the bursts and hosts the collapsing star can be identified, and
their afterglows are complex and differ from one the distance of the GRB from Earth measured
to the next. Any theory for the origin of γ-ray from the galaxy’s spectrum. Short GRBs, which
bursts must account for both the commonali- typically last less than 2 seconds, are better
ties and the differences between them. Writing explained by two neutron stars bound in a tight
in this issue, Campana et al.2 (page 69) and binary system. The stars produce gravitational
Thöne et al.3 (page 72) use two completely dif- waves and eventually merge to form a black
ferent models to explain the especially unusual hole, producing the GRB’s jets and afterglow
‘Christmas’ γ-ray burst, so dubbed because it in the process of merging.
occurred on Christmas Day 2010. As GRB research has progressed, established
Although each one is a unique event, γ-ray models have been challenged by observations,
bursts (GRBs) can be roughly divided into two even of a single GRB. It is conceivable that the
classes — long and short — according to the GRB population has been ‘polluted’ — or, alter-
duration of the prompt emission. Long GRBs, natively, enriched — by a few puzzling events
which last from 2 seconds to a few minutes, that mimic GRBs but have a completely dif-
are thought to originate from hypernovae, an ferent origin. One such event is the Christmas
unusual class of supernova. They involve the GRB, which was detected by the Swift satellite
collapse of a massive star (a hundred times and is known technically as GRB 101225A.
more massive than the Sun) that not only The Christmas GRB’s γ-ray emission was
explodes as a supernova, but also generates two exceptionally long — it lasted for at least half
opposing high-speed jets of particles, leaving an hour — and the X-ray afterglow faded
behind a black hole. If one of the jets happens much faster than usual, an observation that is
1 D E C E M B E R 2 0 1 1 | VO L 4 8 0 | NAT U R E | 4 7
© 2011 Macmillan Publishers Limited. All rights reserved

2. RESEARCH NEWS & VIEWS
incompatible with prevailing GRB models. The data for the Christmas GRB and found that a compute the likelihood of each hypothesis,
energy spectrum of the afterglow displayed a model in which a minor body of 5 × 1020 grams and perhaps discard one on the basis of statis-
shape (the Planckian form) that is characteris- falls onto a neutron star in our Galaxy is tical considerations. Unfortunately, however,
tic of a plasma whose electrons arrive at such an in excellent agreement, in both temporal such a computation would inevitably involve
equilibrium that we can say that it has a certain and spectral behaviour, with the data. considerable conjecture.
temperature. Conversely, typical energy spec- Both hypotheses2,3 are plausible and explain In short, not much more can be said about
tra of GRBs and their afterglows follow power numerous and complex data. But at least one the nature of the Christmas GRB — except that
laws that well describe the collision of materials is wrong and the definitive proof — namely, the odds are that the event is a rare phenom-
at high velocities, such as that resulting from unambiguous determination of the GRB’s enon that looks like a GRB but falls outside this
the impact of an explosion on its environment. distance from Earth — is missing. Thöne and category. Whatever the case, it’s hard to escape
If the Christmas GRB originates from a colleagues’ study raises several questions. the fascination of a possible comet death on
remote hypernova, as do long-lasting GRBs, How many binaries pass through a phase Christmas Day. ■
why is it so unusual? Could it be a completely of a common envelope and produce GRB-
different phenomenon, only apparently similar like explosions? Do all jets emerge from the Enrico Costa is at IASF-Roma, INAF, Via del
to a GRB? So far, observations have not unam- envelope, or is that the case for only a few of Fosso del Cavaliere 100, 00133 Roma, Italy.
biguously disclosed a host galaxy. The loca- them? How highly collimated is the jet? But e-mail: enrico.costa@iasf-roma.inaf.it
tion of the GRB in the sky is such that it could Campana and colleagues’ study also opens
1. Costa, E. et al. Nature 387, 783–785 (1997).
belong to the Perseus arm of the Milky Way, up queries. How many minor bodies pass in 2. Campana, S. et al. Nature 480, 69–71 (2011).
but also to a satellite of the Andromeda galaxy. close proximity to neutron stars? And is the 3. Thöne, C. C. et al. Nature 480, 72–74 (2011).
In their studies, Campana et al.2 and Thöne deduced mass for the minor body conceiv- 4. Barkov, M. V. & Komissarov, S. S. Mon. Not. R.
et al.3 and set out to address these questions able? The proposed mass is relatively large Astron. Soc. 415, 944–958 (2011).
5. Harwit, M. & Salpeter, E. E. Astrophys. J. 186,
and to explain the origin of the GRB. (and consequently rare) for an object in the L37–L39 (1973).
Thöne et al.3 interpret a change in slope and Solar System, but larger bodies have actually 6. Lodato, G. & Rossi, E. M. Mon. Not. R. Astron. Soc.
colour of the Christmas GRB afterglow’s opti- been found to orbit neutron stars. We could 410, 359–367 (2011).
cal emission as being due to the addition of a
supernova that emerges after 10 days, when the
afterglow has almost vanished. By comparing EA RTH SC I EN CE
the system with similar composite supernova–
GRB objects, they derive a distance for the sys-
tem of 1.6 gigaparsecs and an energy of about
1.4 × 1051 erg, compatible with a typical GRB.
Redox state of
early magmas
Thöne and colleagues posit that the GRB
originates from a tightly bound binary system
composed of a neutron star and a supergiant
helium star. The helium star would transfer
mass to the neutron star, and the system would A study of cerium in zircon minerals has allowed an assessment of the redox
evolve to a phase in which the stars would be conditions that prevailed when Earth’s earliest magmas formed. The results suggest
surrounded by a common gas envelope pro- that the mantle became oxidized sooner than had been thought. See Letter p .79
duced by the expansion of the external layers
of the helium star. The neutron star and the
core of the helium star would merge to form B R U N O S C A I L L E T & FA B R I C E G A I L L A R D and deep interior of our dynamic planet has
A
a black hole or a highly magnetized neutron inevitably resulted in the loss of evidence of
star, known as a magnetar4, producing a GRB- prime goal of petrologists has been to Earth’s ancient composition. In this respect,
like jet that would eventually emerge through assess the redox conditions of magmas Earth contrasts sharply with other planetary
the common envelope. The authors find that produced throughout Earth’s evolu- objects — particularly the Moon and Mars,
this model agrees with the observed thermal tion, because magmas are known to affect which are largely unaffected by large-scale geo-
spectrum of the GRB. However, the case for various major phenomena — such as the dynamics. Thanks to the Apollo programme
the additional supernova, which would be composition of volcanic emanations, which and to meteorites inferred to be of Martian
unusually faint, is not compelling. There- are widely believed to affect the composition origin, we have rock samples that provide direct
fore, the deduced GRB distance from Earth of the atmosphere1. But research efforts have testimonies of the Moon and Mars’s very early
is uncertain. Moreover, it isn’t clear whether a been hampered by the lack of rocks from the past. But the same cannot be said of Earth.
host galaxy exists. The only optical object seen Hadean eon, which encompasses nearly the Nevertheless, it is generally assumed that all of
near the position at which the GRB took place is first half-billion years of Earth’s existence. these bodies were chemically reduced when
point-like and extremely faint: were it a galaxy it On page 79 of this issue, Trail et al.2 report they first formed and then underwent either a
would be the faintest ever to host a GRB. their analysis of the sole mineral survivors of gradual or stepwise oxidation3.
Meanwhile, Campana et al.2 revive a model the Hadean, zircon samples more than 4 bil- One of the main arguments for a reduced
proposed5 in 1973, soon after the discovery of lion years old. Their findings allowed them to start is that, during or soon after accretion,
GRBs. In this model, a minor body, such as a determine the ‘fugacity’ of oxygen in Hadean Earth must have entered a magma-ocean stage,
comet or an asteroid, flying by a neutron star magmatic melts, a quantity that acts as a meas- when a sizeable part of the planet was molten
at a distance of less than 5,000 kilometres, gets ure of magmatic redox conditions. Unexpect- because of the energy released by accretion
tidally disrupted, breaks into fragments and edly, the zircons record oxygen fugacities processes3. A massive segregation process must
produces a multi-peak GRB. The authors2 used identical to those in the present-day mantle, then have occurred that separated metals from
recent models for tidal-disruption events6 and leading the authors to conclude that Hadean silicates, thus allowing the formation of the
further assumed that the debris of the minor volcanic gases were as highly oxidized as those metallic core and the silicate-containing man-
body forms a transient disk around the star. emitted today. tle. The formation of Earth’s core is thought to
They compared these models with the available The continuous reshaping of the surface have occurred 30 million to 60 million years
4 8 | NAT U R E | VO L 4 8 0 | 1 D E C E M B E R 2 0 1 1
© 2011 Macmillan Publishers Limited. All rights reserved