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Listening for the 'birth cries' of black holes

Jonathan Amos | 15:14 UK time, Tuesday, 20 April 2010

We're talking about the astronomical stuff of nightmares - gargantuan explosions that rip apart giant stars to create black holes.

Artist's impression of jets emerging from a dying starThese events are detected in space every few days thanks to Nasa's Swift observatory.

The spacecraft sits above the Earth hunting for gamma-ray bursts (GRBs), the intensely bright but fleeting flashes of very high-energy radiation that can sweep our way from all points in the sky.

It's not just imploding stars that emit GRBs; colliding dead stars and black holes can also produce these high-energy "flashbulbs".

When Swift detects one, it swings itself to look directly into the burst with X-ray and ultraviolet/visible telescopes. It also sends out an alert asking other space and ground-based facilities to train their eyes on the event, to analyse the "afterglow" at many different wavelengths.

Launched in 2004, Swift has been a tremendously successful endeavour that has just bagged its 500th GRB (an event that has been given the not-so-catchy designation GRB 100413B).

It's one of those missions in which the UK has won for itself an important role even though in cash terms its contribution has been relatively small.

Artist's impression of Swift in spaceJust as with two of Nasa's recent Sun missions - Stereo and the Solar Dynamics Observatory - Britain has provided key bits of kit for Swift.

The X-ray camera and elements of the ultraviolet/optical telescope come from these shores. Indeed, they included spare parts left over from Europe's X-ray space telescope, XMM. How British is that?

Data processing and archiving is also done here, with much of the effort led out of the University of Leicester.

So what have we learnt from Swift? Well, the mission has certainly put some observational flesh on the theoretical bones.

There have been many uncertainties and mysteries surrounding GRBs since their first detection in the 1960s (the Americans initially thought they might be coming from secret Soviet bomb tests!).

Scientists like to talk about "long bursts" and "short bursts".

Long ones - those that last more than a couple of seconds - we're pretty certain now come from end-stage stars collapsing in on themselves to form black holes. The implosion of these beasts produces superfast jets of material that punch their way out of the dying star into space. Dr Julian Osborne from Leicester takes up the story:

"The gamma-rays are generally thought to be due to what are called internal shocks. You have a jet of material coming out of the star and this jet is supposed to be somehow stuttering, and collisions within the jet in the various stutters are thought to be the cause of the gamma-ray pulses themselves. It's like the 'birth cries' of the black hole, if you like. It's then the collision of that jet with the surrounding medium [beyond the star] that is thought to generate the afterglow - the much longer lived, days to weeks, X-ray and optical emission."

Short GRBs - ones that last less than a couple of seconds - probably have a more varied genesis.

Some may come from compact, super-magnetic remnants of dead stars known as magnetars. It's hard to envisage these objects. Think of something about the mass of our Sun confined in a space about the size of London with a magnetic field quadrillions of times more powerful than the Earth. Bizarre.

Another key source is probably the merging of other dead-star remnants (neutron stars). These are a key source for study now because their coalescence should be accompanied by the emission of gravitational waves.

Huge machines have been built to try to detect these long-sought ripples in the fabric of space-time predicted by Einstein, and every time Swift clocks a GRB, it alerts the gravitational wave hunters so they can look through the squiggly lines in their data for any hint of a signal.

Artist's impression of gravitational wave generation

Scientists hope GRBs might lead them to detect gravitational waves

One of Swift's great achievements, though, has been in pushing back our understanding of the really deep Universe.

On 23 April last year, Swift detected GRB 090423 in the Constellation Leo.

This burst holds the record for being the most distant object yet seen in the Universe. Its flash covered a staggering 13.04 billion light-years to reach us.

If you consider the cosmos is about 13.7 billion years old, it means the star that produced GRB 090423 could have been among the very first to shine in the Universe. Julian says:

"The most distant objects known in the Universe are now gamma-ray bursts. It's these that really demonstrate the importance of GRBs for astronomy and cosmology, because they take us to an evolutionary phase in the Universe that we know very little about indeed. Identifying the most distant galaxies tells us about galaxy formation and the first generation of stars, perhaps. It's an era we struggle to see any other way."

Swift has a good few years left in it. It has no consumables onboard, no propellants or coolants that could run out. It runs the usual risks of course - its X-ray telescope has already been hit by a micrometeorite - but there's every reason to believe it can continue to function throughout most of this decade.

For the UK contribution too, there is optimism. Although UK Swift will get 20% less funding in future, it survived the recent cull in operational monies that support British involvement in several other high-profile missions: Cassini, Cluster, Soho, Venus Express, and XMM.

I blogged about this set-back for UK space science in February. However, I'm pleased to report that since that posting a possible solution has emerged which would see the European Space Agency pick up some of the UK costs of these missions. This should be confirmed in the coming months.

Watch this space.


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  • 1. At 5:09pm on 20 Apr 2010, ghostofsichuan wrote:

    Some day we may have to wrap our head around the idea of "no beginning and no end." What we call the beginning may only be for what we know and may have happened many times before. Like dark energy, it may be an undetectable force, it may be a force of "nothing". Because we do not understand does not mean that it doesn't exist.

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  • 2. At 08:31am on 21 Apr 2010, Jonathan Amos wrote:

    If you click here you can see a very nice map showing the locations on the sky of all 500 of Swift’s GRBs.

    Some are circled. These are particularly notable bursts:
    GRB 100413B – the 500th
    GRB 090423 – the most distant
    GRB 080319B – bright enough at optical wavelengths to have been seen briefly by the naked eye.
    GRB 070714B - another distant one, some 7.3 billion light-years away
    GRB 060218 – a very close one, just 450 million light-years away
    GRB 050904 – at 12.77 billion light-years, this one was a distance record holder for a while.
    GRB 050509B – One of Swift’s great contributions has been allowing scientists to study the afterglows of short bursts. This was the first.
    GRB 041217. The very first burst detected on 17 December, 2004

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  • 3. At 6:09pm on 21 Apr 2010, Stephen Ashworth wrote:

    So is the 450 million l.y. GRB the closest? It appears that we don't seem to get them within our Galaxy or even local cluster. Or more likely we haven't been looking long enough. How close would one have to be to pose a health risk on Earth, and how frequently would they occur -- do we know yet?

    I presume they estimate the distance by the redshift, assuming that the redshift is purely due to the Hubble expansion of the universe. I've never quite been able to understand the Hubble expansion. If space itself was expanding, then so would all measuring instruments. So presumably the expansion of space is measured relative to the electrical forces that hold material measuring rods together? I may have to go back to university to get this sorted out!

    Anyway, thank you for keeping us up to date on the lower-profile things that are going on, as well as the headline stuff on Constellation.


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  • 4. At 09:05am on 22 Apr 2010, Jonathan Amos wrote:

    @Stephen. Yes, I believe this may well be the nearest recorded by Swift. As the mission's name suggests, the spacecraft's rapid response to a burst means the follow-up observations can catch the afterglow and make the distance measurement. It is ground telescopes - not Swift - that make the infrared studies necessary to do the job. As you say, these distances are described by the way the light from the bursts have been redshifted. For example, the analysis of the light spectrum confirmed GRB 090423 had a redshift of 8.2.

    Fortunately, most of these energetic events are a long way away. Too close and they would fry our atmosphere. Neil Gehrels, Swift's lead researcher, co-authored a paper a number of years ago which considered whether the Ordovician extinction was the consequence of a nearby GRB. The team talked of a GRB within 6,000 light-years of Earth.

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  • 5. At 1:48pm on 25 Apr 2010, aristotles23 wrote:

    Firstly,the term black"hole",is erroneous,these so-called "holes" are anything but.The term singularity,is far more appropriate,as I shall endeavour to explain..When a star collapses in on itself and is in the throes of becoming a singularity,it reaches the stage we are most fascinated with,the accumulation stage.In accumulation,a singularity develops super-strong "gravitational" pull..At a certain point,all atoms travelling inwards are stripped of their electron "shield" and the atomic nuclei are jammed together to form the densest object in existence,the centre of a singularity..The increasing pull during accumulation becomes exponential until there is no more matter near enough to be pulled in,this leads to the next stage,dormancy.The dormant stage will last for a very long time if there is insufficient latent energy in the captured material.The next stage is the one that we might call a "big bang",if we could witness it.Once a singularity has accumulated enough material it will arrive at the point when it's weight over it's mass times it's volume creates a contradiction of the laws of physics and it explodes..At no time was there a "hole",only the most dense almost motionless core,so powerful in its pull that even (visible spectrum) light cannot escape.

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  • 6. At 3:14pm on 25 Apr 2010, aristotles23 wrote:

    Further to my previous comments on "Black holes",It is the case that the star that is too weak,has used up too much energy burning brightly,will collapse in on itself and become a Singularity.After Accumulation,possible Dormancy and ultimately more Accumulation,the singularity will explode. At the point of explosion,the Singularity will create a new Galaxy,at the very least,and is,then,a Galactic recycling point for waste material that is just drifting about in space.In essence,in does not matter that some stars do not have the power to become Supernovae,Galaxies are formed either way,Singularities take a bit longer,but may prove to be a counterpart to Supernovae in the creation of Galaxies,possibly creating materials unique to the exploded Singularity,certainly generating unique circumstances for the production of Galaxies.Even accepting that space is infinite but material finite,the constant recycling of materials in these two ways,means that,Galaxies will always die and Galaxies will always be born.Total Universal Expansion,can be easily explained.All the Galaxies are moving away from each other at an exponentially faster and faster rate,In a Spherical Expansion.At the core of this spherical universe,there is an absolutely massive Singularity,probably the size of several Galaxies,and when its finished its Accumulation,it will explode...again..and not for the first time..This is the Universal Constant.

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