## Newest X-Ray Observatory Will Hunt for Black Holes and More

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The next launch of a NASA space mission is the Nuclear Spectroscopic Telescope Array, or NuSTAR. It study wide range of objects in space, from massive black holes to our own Sun, and will be the first space telescope to create focused images of cosmic X-rays with the highest energies.

“We will see the hottest, densest and most energetic objects with a fundamentally new, high-energy X-ray telescope that can obtain much deeper and crisper images than before,” said Fiona Harrison, the NuSTAR principal investigator, who has been working on this project for 20 years.

Meanwhile, NASA has cancelled another X-ray telescope, the Gravity and Extreme Magnetism Small Explorer (GEMS) X-ray telescope, an astrophysics mission that was going to launch in 2014 to observe the space near neutron stars and black holes. GEMS failed meet a the qualifications of a confirmation review and was heading to go over budget.

“The decision was made to non-confirm GEMS,” said Paul Hertz, director of NASA’s Astrophysic Division, at a meeting of the National Research Council’s Committee on Astronomy and Astrophysics. “The rationale was that the pre-confirmation cost and schedule growth was too large.” The project was going well over the initial cost of $105 million and was facing a delay in launch.

But NuSTAR is scheduled to launch on June 13 from the Kwajalein Atoll in the Pacific Ocean near the equator. The X-ray space telescope will initially take off on a L-1011 “Stargazer” aircraft, and then launch in midair into orbit on a Pegasus XL rocket from Orbital Sciences.

The mission has been awaiting launch since March, when NASA delayed its liftoff pending a review of the rocket.

NuSTAR will work with other telescopes in space now, including NASA’s Chandra X-ray Observatory, which observes lower-energy X-rays. Together, they will provide a more complete picture of the most energetic and exotic objects in space, such as black holes, dead stars and jets traveling near the speed of light.

This new observatory looks with X-rays similar to the X-rays used in hospitals and airports, but the telescope will have more than 10 times the resolution and more than 100 times the sensitivity of previous telescopes.

“NuSTAR uses several innovations for its unprecedented imaging capability and was made possible by many partners,” said Yunjin Kim, the project manager for the mission at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We’re all really excited to see the fruition of our work begin its mission in space.”

NuSTAR has an innovative design using a nested shell of mirrors to provide better focus. It also has state-of-the-art detectors and a large 33-foot (10-meter) mast, which connects the detectors to the nested mirrors, providing the long distance required to focus the X-rays. This mast is folded up into a canister small enough to fit atop the Pegasus launch vehicle. It will unfurl about seven days after launch. About 23 days later, science operations will begin.

The mission will focus on studying the formation of black holes and investigate how exploding stars forge the elements that make up planets and people, along with study the Sun’s atmosphere.

Sources: JPL Space News (GEMS)

Missions, NuSTAR, X-ray astronomy

That’s exciting news. Can hardly wait for first light!

Counting the number of black holes in the universe is important to get an estimate on the average Weyl curvatures in local regions. This is by Penrose’s analysis a measure of the entropy of the universe. I am presuming the survey will be of galactic black holes. These huge black holes have the greatest amount of entropy S = kA/4L_p^2 in the universe. Here A is the area, proportional to the square of the mass of the black hole, and L_p is the Planck length L_p^2 = G?/c^3, and k = 3.8×10^{-23}j/K is the Boltzmann constant. Clearly galactic sized black holes dominate the entropy of the universe in the form of black holes.

LC

Counting the number of black holes in the universe is important to get an estimate on the average Weyl curvatures in local regions. This is by Penrose’s analysis a measure of the entropy of the universe. I am presuming the survey will be of galactic black holes. These huge black holes have the greatest amount of entropy S = kA/4L_p^2 in the universe. Here A is the area, proportional to the square of the mass of the black hole, and L_p is the Planck length L_p^2 = G?/c^3, and k = 3.8×10^{-23}j/K is the Boltzmann constant. Clearly galactic sized black holes dominate the entropy of the universe in the form of black holes.

LC

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Say, that is interesting. I didn’t know about Penrose’s Weyl curvature hypothesis which is supported by black hole dominating entropy:

“On the one hand one would like to account for a Universe which on its largest observational scales appears remarkably spatially homogeneous and isotropic in its physical properties (and so can be described by a simple Friedmann-Lemaître model), on the other hand there is the deep question on the origin of the second law of thermodynamics.

Penrose suggests that the resolution of both of these problems is rooted in a concept of the entropy content of gravitational fields. Near the initial cosmological singularity (the Big Bang), he proposes, the entropy content of the cosmological gravitational field was extremely low (compared to what it theoretically could have been), and started rising monotonically thereafter. This process manifested itself e.g. in the formation of structure through the clumping of matter to form galaxies and clusters of galaxies. Penrose associates the initial low entropy content of the Universe with the effective vanishing of the Weyl curvature tensor of the cosmological gravitational field near the Big Bang. From then on, he proposes, its dynamical influence gradually increased, thus being responsible for an overall increase in the amount of entropy in the Universe, and so inducing a cosmological arrow of time.”

This strong (predictive!) hypothesis of Penrose is a contender to standard cosmology inflation. And incidentally it also replaces such hypotheses for the cosmological arrow of time as cosmological expansion, which are my favorites as they are simple.

So it bothered me, and since I haven’t really considered the cosmological components of entropy but naively assumed CMB entropy dominated I managed to immediately find this paper of Frampton, Hsu et al (with input from Maldacena, no less) on the entropy of the universe from 2009. They describe how unitarity conservation makes black hole entropy much smaller than the thermodynamical macroscale limit:

“Ordinary matter (star, galactic core, etc.) collapses to form an astrophysical black hole. Under unitary evolution, the number of ?nal Hawking radiation states that are actually accessible from this collapse is ~ expM^ 3/2 , i.e. precisely the number of ordinary astrophysical precursors (3). It is therefore much smaller than the the number of expM^2 states a

black hole, and its eventual Hawking radiation, could possibly occupy if nothing about its formation process were known.”

This makes the CMB entropy the dominating entropy of an inflationary universe. And according to them it must be so:

“Finally, there is a trivial cosmological argument … Now consider the era of decoupling, when CMB photons decoupled from atoms. In conventional big bang cosmology, there were no black holes in the universe during that epoch. At decoupling, the entropy of thermal photons (and perhaps neutrinos) vastly dominated over all other forms, and consequently the entropy of the CMB modes must still dominate today [23].”

Footnote: “[23] The number of degrees of freedom of all other systems is tiny compared to that of the CMB (including neutrinos; see Table I without black holes). For this reason only a negligible part of the entropy of the thermal photons and neutrinos could, since the era of decoupling, have been dumped into other forms or into entropy of entanglement with other systems.”

Frankly I find Penrose’s ideas here non-intuitive. How could one innate and conservative process take over and dominate entropy production? Far easier for me to believe it has been the result of (re)heating as inflation put on the brakes (finally ended) in local universe, then slowly leaking over to structures from structure formation while diluting as the universe expands.

So, a strong hypothesis, I assume the math works out, black holes are considered dominating the entropy by most I take it. But I like my unitarity where I can find it.

I thought about going into some of this, but I did not have the time to write a really long post. I probably should have indicated the Weyl curvature is a more local result.

You might notice in that paper the list of elements in the universe and their contribution to entropy and the contribution to ? contribution to the matter in the universe. Supermassive black holes weigh in with entropy S = 10^{102} and ? = 10^{-5} and the cosmological Bekenstein or holographic bound is S = 10^{123} and ? = 1, which really should be more like ? ~= 1 – 10^{-5}. The contribution of holographic bound occurs on the largest scales of the universe. This is the distance to the particle horizon at ? = ?dt/a(t) which is around 500 billion light years. This is the limit of observability, which is different from the cosmological horizon that is the limit which prevents us from sending a signal out to. Any galaxy with z > 1 and beyond the cosmological horizon we will never be able to send information to, though we can receive information sent from these galaxies in the past. The CMB is out around z = 1000. So clearly on the grandest scale the holographic bound is the ultimate entropy.

The Weyl curvature hypothesis of Penrose says the major contribution to entropy locally is the curvature induced by black holes with non-zero Weyl curvature. This is the major contribution to entropy in a local region, say out to z < 1. As the scale of the universe is examined out to z = 1 and beyond the dynamics of space begin to dominate the structure of the universe far more than local curvatures from galaxies or black holes. This is a feature of the de Sitter spacetime of the universe. When Penrose advanced the Weyl curvature hypothesis (around 1980) it was commonly thought the universe was a recollapse system with k = 1 in the FLRW metric. In this perspective the universe would reach a maximum radius of expansion and then recollapse into the big crunch. The Weyl curvature from the clumping of matter would increase on average through the evolution of such a spacetime. However, the spacetime frame Penrose worked in has been found to be wrong.

In this particular paper http://arxiv.org/pdf/1205.4710v1.pdf the recollapse model exceeds the holographic bounds and in a quantum cosmological setting there is a phase transition from a k = 1 type of spacetime to inflationary de Sitter spacetime. V. Cardenas initially observed this violation of the holographic bound arXiv:0908.0287v1 [gr-qc], which makes the spacetime Penrose invoked impossible.

However, the Weyl curvature conjecture is still a worthwhile physical concept for galactic astrophysics. The thermodynamic process which drives galaxies, clusters of galaxies and so forth is probably well in line with Penrose’s hypothesis. This might include the formation of dark matter filaments and the rest.

LC

Thanks for the response! I’m not sure my comment warranted one, except for the problems and misunderstandings you uncover.

I understand that using the Weyl curvature to get an estimate of SMBH entropy is different from Penrose’s curvature hypothesis. I worded my comment poorly. Thanks for pointing out that the hypothesis is obsolete! Ironic if inflation subjugates, so to speak, the spacetime he used.

As for the holographic bound, I’m not sure I follow. If holography is the AdS/CFT correspondence, it should incorporate all entropy and not specifically contribute as I understand it.

A handle on (local) gravitational thermodynamics, nice observation.

If the Weyl curvature were absolutely zero everywhere the CMB would be perfectly isotropic. Small nonzero Weyl curvatures in the universe are the source of the anisotropy in the CMB. The Weyl curvature hypothesis is then a sort of local approximation rather than a primary physical principle. Further, the entropy measured in the Weyl curvature is eventually absorbed by the holographic bound. Black hole quantum mechanically decay leaving space flat again. The information contained in the black hole, or concealed as entropy, is absorbed by the entropy at the Bekenstein or holographic bound.

LC

While there is bad news for the Gravity and Extreme Magnetism Small Explorer (GEMS) X-ray telescope team, it’s refreshing to see NASA’s Astrophysics Division taking a hard line. There must be no more JWST style delays, budget blow outs or collateral-damage cancellations, so stick to your time lines Goddard or else.

…and good luck for June 13th NuSTAR.

Sharper X-ray images, me likey.

X-ray mirror optics, an interesting side topic now finally coming into astronomical fruition, nearly stealing the show of this experiment for me.

Okay, black hole & jet studies are exciting too.

Well, hopefully all will go well. It would be fully operational next year, when it will certainly be turned to the dark side… oh, sry… I meant the Galactic Center. I am still quite excited about that gas cloud coming in…