Category: Relativity

No Naked Singularity After Black Hole Collision

Black holes cannot be naked... the event horizon will always be there to cover them up...
Black holes cannot be naked... the event horizon will always be there to cover them up...

You can manipulate a black hole as much as you like but you’ll never get rid of its event horizon, a new study suggests. This may sound a little odd, the event horizon is what makes the black hole, well… black. However, in the centre of a black hole, hidden deep inside the event horizon, is a singularity. A singularity is a mathematical consequence, it is also a point in space where the laws of physics do not apply. Mathematics also predicts that singularities can exist without an associated event horizon, but this means that we’d be able to physically see a black hole’s singularity. This theoretical entity is known as a “naked singularity” and physicists are at a loss to explain what one would look like.

Like any good physics experiment, an international team from the US, Germany, Portugal and Mexico have decided to simulate the most extreme situation possible in the aim of stripping a pair of black holes of their event horizons. They did this by constructing an energetic collision between two black holes travelling close to the speed of light, crashing head-on. Here’s what they discovered…
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Flyby Anomalies Solved?

When the Galileo probe used the Earth for a gravitational slingshot, an anomaly in its velocity was observed (NASA)
When the Galileo probe used the Earth for a gravitational slingshot, an anomaly in its velocity was observed (NASA)

This is a captivating mystery. In 1990 and 1992 when the Jupiter probe Galileo used the Earth for gravitational assists (or “slingshots”), ground-based observers noticed a small (unexpected) boost in velocity as the spacecraft approached Earth. A boost in a few millimetres per second had also been observed in the slingshot of NASA’s NEAR probe two years previously. The same was seen in the flybys of Cassini (in 1999), MESSENGER and Rosetta (in 2005). Many explanations have been put forward – including my favourite that it could be dark matter in Earth orbit kicking our robotic explorers around – but flyby anomalies may have a more mundane explanation.

In keeping with Occam’s Razor (i.e. the simplest explanation is usually the right one), a short paper has been published suggesting that flyby anomalies can be accounted for by using conventional physics…
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Could Warp Drive Become a Reality?

The physics behind the warp drive (Richard Obousy and Gerald Cleaver)
The physics behind the warp drive (Richard Obousy and Gerald Cleaver)

In science fiction, the “warp drive” helps Captain Kirk, Jean-Luc Picard, Commander Janeway and Benjamin Sisko potter around space with ease. Without warp speed, TV episodes of Star Trek would stretch into months and seasons would last decades. Alas, even science fiction succumbs to the laws of relativity: Nothing, not even light (or a Klingon) can travel faster than the speed of light. As I researched for a recent Universe Today article, the space between the stars is prohibitively large, even the nearest star is over 4 light years away (Proxima Centauri), so how could it be possible for USS Enterprise to flit from one star system to the next without putting a dent in Einstein’s theory of relativity? The answer comes if we realise that although light speed is a physical limit on how fast things can travel through space-time, there is no limit on how fast space-time can travel if it is warped. Suddenly we have a theoretically possible means of travelling between the stars by altering the fabric of the Universe in a warp “bubble”…
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The Sinister Side of the Cosmos: Killer Galaxies, Cosmic Forensic Science and Deadly Radiation

The ghost of a dead dwarf galaxy hangs around the killer, spiral galaxy (R. Jay Gabany)

It’s been a busy day with a range of topics posted on the Universe Today, but all have a common thread: the universe is a deadly place for man and galaxy. For starters, research into the radiation mankind will face when settling on Mars and the Moon could prove to be one of our main challenges in space. The threat of a massive dose of radiation from a solar flare is bad enough, but the gradual damage to our cells and increased risk of cancer is a problem we need to solve, or at least manage. But that’s nothing compared with what dwarf galaxies have to put up with; their larger spiral cousins like to eat them for dinner, leaving behind galactic ghosts of the dwarfs that were…
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When Stars Collide: LIGO and Gravitational Wave Astronomy

Binary black holes generating gravitational waves. Image credit: Image Credit: K. Thorne (Caltech), T. Carnahan (NASA GSFC). Source: http://lisa.jpl.nasa.gov/gallery/binary-wave.html

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is an ambitious project. The experiment is designed to detect and characterize gravitational waves generated by energetic and massive events in the cosmos. What’s more, as LIGO has two stations situated 3000 kilometres (1870 miles) apart, through triangulation, the location of a star collision or black hole event can be deduced in the sky. Completed two years ago, LIGO has been taking data ever since and the time has now come to begin analysing the results, seeing if the theoretical gravitational wave can actually be observed, bringing us into a new era of astronomy, gravitational wave astronomy…
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Will Time be Replaced by Another Space Dimension?

Space-time cones - what if time were to disappear?

What if time disappeared? Yes, it sounds like a silly question – and if the cosmos sticks to the current laws of physics – it’s a question we need never ask beyond this article. Writing this article would in itself be a waste of my time if the cosmos was that simple. But I’m hedging my bets and continuing to type, as I believe we have only just scratched the surface of the universal laws of physics; the universe is anything but simple. There may in fact be something to this crazy notion that the nature of the universe could be turned on its head should the fundamental quantity of time be transformed into another dimension of space. An idea like this falls out of the domain of classical thought, and into the realms of “braneworlds”, a view that encapsulates the 4-dimensional universe we know and love with superstrings threaded straight through… [more]