Universe – Page 4 – astroengine.com

Unexpectedly Large Black Holes and Dark Matter

The M87 black hole blasts relativistic plumes of gas 5000 ly from the centre of the galaxy (NASA)

I just spent 5 minutes trying to think up a title to this post. I knew what I wanted to say, but the subject is so “out there” I’m not sure if any title would be adequate. As it turns out, the title doesn’t really matter, so I opted for something more descriptive…

So what’s this about? Astronomers think they will be able to “see” a supermassive black hole in a galaxy 55 million light years away? Surely that isn’t possible. Actually, it might be.

When Very Long Baseline Interferometry is King

Back in June, I reported that radio astronomers may be able to use a future network of radio antennae as part of a very long baseline interferometry (VLBI) campaign. With enough observatories, we may be able to resolve the event horizon of the supermassive black hole lurking at the centre of the Milky Way, some 26,000 light years away from the Solar System.

The most exciting thing is that existing sub-millimeter observations of Sgr. A* (the radio source at the centre of our galaxy where the 4 million solar mass black hole lives) suggest there is some kind of active structure surrounding the black hole’s event horizon. If this is the case, a modest 7-antennae VLBI could observe dynamic flares as matter falls into the event horizon.

It would be a phenomenal scientific achievement to see a flare-up after a star is eaten by Sgr. A*, or to see the rotation of a possibly spinning black hole event horizon.

All of this may be a possibility, and through a combination of Sgr. A*’s mass and relatively close proximity to Earth, our galaxy’s supermassive black hole is predicted to have the largest apparent event horizon in the sky.

Or does it?

M87 Might be a Long Way Away, But…

As it turns out, there could be another challenger to Sgr. A*’s “largest apparent event horizon” crown. Sitting in the centre of the active galaxy called M87, 55 million light years away (that’s over 2,000 times further away than Sgr. A*), is a black hole behemoth.

M87’s supermassive black hole consumes vast amounts of matter, spewing jets of gas 5,000 light years from the core of the giant elliptical galaxy. And until now, astronomers have underestimated the size of this monster.

Karl Gebhardt (Univ. of Texas at Austin) and Thomas Jens (Max Planck Institute for Extraterrestrial Physics in Garching, Germany) took another look at M87 and weighed the galaxy by sifting through observational data with a supercomputer model. This new model accounted for the theorized halo of invisible dark matter surrounding M87. This analysis yielded a shocking result; the central supermassive black hole should have a mass of 6.4 billion Suns, double the mass of previous estimates.

Therefore, the M87 black hole is around 1,600 times more massive than our galaxy’s supermassive black hole.

A Measure for Dark Matter?

Now that the M87 black hole is much bigger than previously thought, there’s the tantalizing possibility of using the proposed VLBI to image M87’s black hole as well as Sgr. A*, as they should both have comparable event horizon dimensions when viewed from Earth.

Another possibility also comes to mind. Once an international VLBI is tested and proven to be an “event horizon telescope,” if we are able to measure the size of the M87 black hole, and its mass is confirmed to be in agreement with the Gebhardt-Jens model, perhaps we’ll have one of the first indirect methods to measure the mass of dark matter surrounding a galaxy…

Oh yes, this should be good.

UPDATE! How amiss of me, I forgot to include the best black hole tune ever:

Publication: The Black Hole Mass, Stellar Mass-to-Light Ratio, and Dark Matter Halo in M87, Karl Gebhardt et al 2009 ApJ 700 1690-1701, doi: 10.1088/0004-637X/700/2/1690.
Via: New Scientist

The Naked Singularity Recipe: Spin a Black Hole, Add Mass

naked_singularity

The event horizon of a black hole is the point of no return. If anything, even light, strays within the bounds of this gravitational trap, it will never escape. The event horizon is what makes a black hole black.

But say if there was a way to remove the event horizon, leaving just the black hole’s singularity to be “seen” by the rest of the universe? What if there is a special condition that would allow this infinitely small, yet massive point to become naked?

Generally physicists agree that this is a physical impossibility, but the mathematics says otherwise; a naked singularity could be possible.

Previously on Astroengine, one “special condition” was investigated when an extreme black hole collision was simulated by a Caltech researcher. In this case, the black hole pair was smashed together, head-on, at a velocity close to the speed of light. The gravitational waves travelling away from the collision were then modelled and characterized. It turns out that after this insanely energetic impact, 14% of the total mass was converted into gravitational wave energy and both black holes merged as one.

While this might not be very realistic, it proved to be a very useful diagnostic tool to understand the conditions after the collision of two black holes. As an interesting observation, the Caltech researchers found that although the collision was extreme, and there was a huge amount of mass-energy conversion going on (plus, I’d imagine, a rather big explosion), neither black hole lost their event horizons.

Case closed, wouldn’t you think?

Actually, another theory as to how a black hole could be stripped naked has been knocking around for some time; what if you added mass to a black hole spinning at its maximum possible rate? Could the black hole be disrupted enough to shed its event horizon?

It turns out there’s a natural braking system that prevents this from happening. As soon as mass is dropped into the black hole, it is flung out of the event horizon by the black hole’s huge centrifugal force, preventing it from coming close to the singularity.

However, Ted Jacobson and Thomas Sotiriou at the University of Maryland at College Park have now improved upon this idea, sending mass in the same direction as the spinning black hole. Only this time, the black hole isn’t spinning at its fastest possible rate, the simulation lets the orbiting matter fall into the event horizon, speeding up its spin. The result? It appears to disrupt the black hole enough to strip away the event horizon, exposing the singularity.

The most interesting thing to come of this research is that swirling matter is falling into black holes all over the universe, speeding up their spin. Jacobson and Sotiriou may have stumbled on a viable mechanism that actually allows naked singularities in the cosmos. Unless nature has found another way to prevent the cosmic censorship hypothesis from being violated that is…

Source: New Scientist

Astroengine Live CANCELLED… Until Next Week

astroengine_live_header

Apologies for the break in Astroengine Live service. Due to some uber-technical problems, I’m going to have to re-launch the show this time next week. Stay tuned for updates.

For now, check out my Astroengine Live archives and enjoy!

***

Earlier post:

It’s been a while, but Astroengine Live is back on the air, TODAY! It’s been a fascinating few weeks, so I want to share some of the stuff I’ve come across. I especially want to go into the current Wide Angle over at Discovery Space, “Surfing Spacetime”.

So tune in to the Badlands Radio feed at 4pm PST/7pm EST and all the timezones in between and far away…

I’ll also be tweeting throughout the broadcast, so feel free to interrupt me on @astroengine.

Did Dark Matter Reionize the Universe?

Did dark matter characterize our early Universe?

Immediately after the Big Bang, 13.72 billion (±120 million) years ago, the Universe was filled with energy. Nothing but energy. No protons, electrons, quarks or photons; just energy. Even the fundamental forces of nature (gravity, weak, strong, electromagnetic) were a confused mess and could not be distinguished, but that issue didn’t last for long. 10^-43 seconds after the Big Bang the grand unification epoch began, when gravity is thought to have separated from the soup. Shortly after, the strong force separated from the electroweak force in a period called the electroweak epoch.
Continue reading “Did Dark Matter Reionize the Universe?”

Mystery Blob Detected 12.9 Billion Light Years Away

Take a good look, this is one of the most mysterious, massive objects ever discovered in the cosmos. We don’t really know what it is, but this thing is huge, spanning 55,000 light years across (the approximate radius of our Milky Way). What makes this all the more intriguing is the fact that this object formed only 800 million years after the Big Bang and it is 10 times more massive than the next biggest object observed in the early Universe. But what is it?
Continue reading “Mystery Blob Detected 12.9 Billion Light Years Away”

Did Gravitational Waves Ring a Bell in 1987?

Gravitational waves generated by a binary system (MIT)

The hunt for gravitational waves continue, but unfortunately all gravitational wave hunters around the world are churning up nothing. Just noise. Could it be that this consequence of Einstein’s theory of General Relativity is horribly flawed? Probably not. Still, the search for these elusive waves has foxed physicists for many years. It has even come to the point that the laser interferometers used in an attempt to detect the tiny (and I mean TINY) changes in distances (as when the gravitational wave passes through us, space-time experiences a minuscule compression or expansion) have become so precise, the director of Fermilab thinks a German-UK gravitational wave detector is starting to detect the quanta of space-time itself.

However, do you ever get the feeling that we might be trying too hard? What if gravitational waves have already been detected? Say if these notoriously difficult ripples in space-time were detected over 20 years ago without using a laser interferometer? It turns out that an overlooked scientist may have found the answer to the gravitational wave problem by using nothing more than some aluminium bars and a well-timed supernova…
Continue reading “Did Gravitational Waves Ring a Bell in 1987?”

Gravitational Waves and Gravity Waves, What’s the Difference?

I’ve received this question so many times, so I thought I’d post, for reference purposes, the difference between a gravitational wave and a gravity wave. Yes, they are different creatures (although many authors would have you believe otherwise).

Gravitational waves are theoretical perturbations (ripples) in space-time. Much work is going into the discovery of gravitational waves using gravitational wave detectors like the US Laser Interferometer Gravitational-Wave Observatory (LIGO) or German-British GEO600, but so far, they have proven to be very elusive. In a previous Astroengine post, there is a new theory that perhaps gravitational wave detectors have reached a limit on their precision (i.e. the quanta of space-time, leading to the holographic universe conjecture). Gravitational waves, as predicted by Einstein’s theory of general relativity, are thought to exist, but have yet to be detected. There are indirect observations of gravitational waves, from observations of the slowing period of binary stars; energy is most likely being lost through gravitational wave generation. Gravitational waves are thought to be generated also by black hole collision, pulsars and supernovae. More on Gravitational Waves…

Gravity waves are physical perturbations driven by the restoring force of gravity in a terrestrial environment. A common example of this are waves formed at an air-water boundary (i.e. the surface of the ocean). Wind creates an instability in the ocean, the restoring gravity force pulls down on the water, while the buoyancy of the water pushes it back up. A perturbation then propagates (i.e. ocean waves). Extreme examples include tsunamis and tides. Perturbations in the atmosphere can also be caused by gravity, where rising/falling air tries to regain equilibrium (after being forced over a maintain range, say), but gravity and buoyancy forces will cause it to propagate as a wave. More on Gravity Waves…

So, gravitational waves are perturbations in space-time (over universal scales). Gravity waves are perturbations in atmospheres (planetary scale). They most certainly are not the same thing.

Is the Universe a Holographic Projection?

Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)

Could our cosmos be a projection from the edge of the observable Universe?

Sounds like a silly question, but scientists are seriously taking on this idea. As it happens, a gravitational wave detector in Germany is turning up null results on the gravitational wave detection front (no surprises there), but it may have discovered something even more fundamental than a ripple in space-time. The spurious noise being detected at the GEO600 experiment has foxed physicists for some time. However, a particle physicist from the accelerator facility Fermilab has stepped in with his suspicion that the GEO600 “noise” may not be just annoying static, it might be the quantum structure of space-time itself…
Continue reading “Is the Universe a Holographic Projection?”

Slacker Astronomy Interviews Dr Michael Turner about Dark Energy

I’m just listening to Slacker Astronomer Michael Koppelman’s excellent interview with Dark Energy’s Dr Michael Turner at last week’s AAS conference in Long Beach. You have to listen to Turner’s views on dark matter, dark energy, the LHC, the rights and wrongs of general relativity and some great opinion about the current state of cosmology. On checking out Turner’s bio on his website, anyone who has “Space” listed under “Areas of Expertise” has to be listened to!

I especially liked the Slacker question concerning the growing number of people opposed to the idea of dark energy accusing cosmologists of “drinking the same Kool Aid” (in reference to the perceived thought that dark energy might be a crazy idea), to which Turner replies with, “Well we do all drink the same Kool Aid, that is true. I’m Mr Kool Aid!”

It is a really entertaining interview, providing an insight to the cutting edge of cosmological thought and excitement for the continuing work being done in the field.

Great work Slacker Astronomy! Now I feel like the slacker, Astroengine.com didn’t manage any podcasts direct from the scene of the AAS… I must remember by dictaphone in June for the next AAS in Pasadena!

Source: Slacker Astronomy

Can Gravitational Waves be Used for Evil?

Theoretical gravitational waves generated after a black hole collision. Can we surf them?

Gravitational waves are a theoretical consequence of a propagating energy disturbance through space-time. They are predicted by Einstein’s general relativity equations, and astrophysicists are going to great pains to try to detect the faint signature from the passage of these waves through local space. Unfortunately, even though millions of dollars have been spent on international experiments, the gravitational wave remains in equation form; there is little (direct) evidence to support their existence.

However, this doesn’t stop the US military from worrying about them and commissioned a 40-page report into whether high frequency gravitational waves could be used by an enemy. Excuse me? Gravitational waves… as a weapon?
Continue reading “Can Gravitational Waves be Used for Evil?”