The loneliest black holes

The loneliest black holes
Supermassive black holes are actively growing in even the emptiest regions of the universe.
Provided by Drexel University

This artist's impression of a supermassive black hole highlights the accretion disk of gas and stars swirling around the black hole, and the jets of material ejected along the poles. Supermassive black holes are found even where galaxies are sparse and interaction is minimal. These black holes accrete matter at a slower rate than black holes in denser galactic environments. A. Kamajian/NASA

This is a tiny extract from a newsletter to me from the Astronomy magazine. The readers may further enrich their knowledge by subscribing to it.

srini

June 6, 2007

In a study of more than 1,000 void galaxies, using data from the Sloan Digital Sky Survey (SDSS-II), astronomers from Drexel and Widener Universities announced that the growth of these monster black holes — with masses millions to hundreds of millions times that of our sun — are found where galaxies are sparse and interact very little with each other. The researchers also found that the accretion of matter onto these void black holes is slower than in denser galactic environments.These findings shed light on the black hole formation and evolution process by showing that the environment does affect how quickly galaxies proceed through their evolutionary cycle. The simple presence of growing supermassive black holes in the rural outposts of the universe challenges the current theoretical models of galaxy and structure formation and evolution, explained Anca Constantin of Drexel University, lead author of the paper delivered last week at the American Astronomical Society meeting in Honolulu. "Interestingly, we see actively accreting galactic black holes in all phases of evolution in these sparse regions," said Constantin. "This means that the black hole growth process is quite similar in what could be compared to the most reclusive countrysides and in the crowded urban regions of the universe." The void regions, nearly empty, three-dimensional fields hundreds of millions of light-years across, fill half of the universe. Only five percent of all galaxies live in these bubble-like regions. The other 95 percent of galaxies live together in communities, crowded into clusters, filaments, and walls: the cities and suburbs of the universe. Studying a 700-million light year wide 'slice' of the universe, the researchers found that spectra of the centers of void galaxies show hot gases ionized by light emitted from matter swirling around supermassive black holes. Constantin adds that, "the more isolated accreting black holes are however not as active as the ones in more populous environs, and the fuel seems less available for accretion in voids than in 'urban' galaxies." Astronomer Fiona Hoyle, a member of the discovery team from Widener University added: "This is strange given that these reclusive galaxies are forming stars at higher rates than their counterparts in denser regions; this means there is plenty of fuel, but it is not efficiently channeled toward the central engine."


Star formation requires the presence of large amounts of gas and so there must be more than enough gas in the void galaxies if their star forming rates are high, explained Hoyle. The smaller accretion rate observed in void galaxies means that this gas is just not getting down to the nuclear region where accretion happens. Interactions with other galaxies are thought to disturb the gravitational potential, which drives some gas into the nuclear region. "These interactions are not as frequent in voids, so the 'feeding' of the black hole is slower." These rugged individuals in voids do not need to compete with their neighbors for fuel, and their life cycle is rarely bothered, noted Constantin. In contrast, life is more hectic in crowded regions where galaxy interactions are frequent. As a consequence, galaxies are either stripped of their gas or more material is funneled toward the central engine. This means that there are many more chances the accretion onto black holes is enhanced or turned off in more 'urban environments.' "On the other hand, the void galaxy black holes might take longer to reach the mature, low accretion rate phase, which might explain why the most massive, lazy black holes are less frequent in voids," she noted. The data studied by Constantin may also show that active black holes appear to be more common in voids but only among small (less massive) galaxies, while less common among massive galaxies. This is also a clue that the life cycle of black hole growth in voids is delayed or slower compared to that in denser regions. Discovery team member Michael Vogeley of Drexel said that it's particularly puzzling that the few most massive and sluggishly accreting void systems live within the most secluded sub-regions, while their "urban" counterparts are found in the most populated neighborhoods. "Perhaps because massive objects are prone to accreting material around them, such a 'cleaning' process would contribute to emptying the already rarefied neighboring space in voids," Vogeley noted. "This would leave little or insufficient material for future formation of other nearby massive, bright galaxies." In contrast, within galaxy clusters where there is plenty of stuff around, accretion of surrounding material would make a small difference. These results have been possible only because of the sheer number of void regions and void galaxies found in the SDSS-II data, the most ambitious survey of the universe ever undertaken, the researchers said. The sample used in the analysis announced last week comprises more than 1,000 void galaxies. Previously, the black hole accretion in centers of void galaxies had been studied in only a handful of objects contained in only one void region, the Bootes Void.

Acknowledgements: Astronomy magazine's newsletter to me

srini

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This too is starscape as seen from Chile observatory. Any guesses about that red one?

srini

This is a picture of stars taken from an observatory in Chile.
What a catch?

srini

Discovery of planets - hoping to find life!

Data collected by NASA's orbiting Spitzer Space telescope on two Jupiter-like gas planets hundreds of trillions of kilometres away - one in the constellation of Pegasus and the other in the constellation of Vulpecula - point towards some vital evidences.

One of the planets had evidence of small sand-like particles, called silicates, in the atmosphere, sugesting it is wrapped in high, dusty clouds unlike any planet in our solar system. Spitzer observed for the first time enough light to figure out signatures of molecules in the atmospheres of planets outside our little one. It was deemed as a step in a long chain of events hopefuly leading to discovering life on some other planet.

These two planets - terrifically hot gas giants whizzing around their stars in alarmingly close orbits were considered to be unlikely to harbour life, presently. But scientists hoped to use similar techniques to scour smaller, rocky planets more like the Earth for indications of life, perhaps in the form of oxygen or possibly chlorophyll. The probability of water being there hidden by a thick layer of clouds, was not ruled out.

Finally, the 'present' must consider the time delay in getting the data - howmany lightyears of distance they are away etc.!

srini

Coming to nuclear density calculations!

Based upon the atomic radius of hydrogen (32 picometres) and the proportion of the volume of nucleus with respect to the total atomic volume (10**-13 approx), the nuclear density of hydrogen is 1/15 that of the core matter achieved after gravitational collapse, which means that the radius of the single proton is about 40% of the radius of the nucleus. But hold! we have to see what similar calculations on atoms of other elements have to say. It could be true that neutrons are smaller than thought to be.
Taking the case of Radon with atomic mass at 222a.m.u. and atomic radius at 140 picometres,
it can be seen that the nuclear density of Radon is about 2.5 times that of hydrogen. That means the protons and neutrons are more closely packed in the nuleus of Radon than in Hydrogen.
One has to do the exercise on sufficient number of samples to arrive at a reliable conclusion!

srini

Further about neutron star and the core of collapsed matter!

Then, it follows that for the typical neutron star discussed earlier, the specific gravity of 5*10**14 yieds a critical radius of 4*10**9 km/sqrt(5*10**14) =180 km approx. Thus the neutron star still falls short of becoming a blackhole (10km radius as against the required 180km). For the collapsed core referred to earlier, the critical radius becomes 180/sqrt(2) km = 127 km, which too should be visible and not a blackhole unless a core of 127 km radius is achieved!

srini

Getting denser!

For gold, r(critical) becomes 0.7*10**9km (a shining blackhole!); for platinum, it is 0.55*10**9km.
Now going a bit celestial, the density of a neutron star is known to be in the range of 0.5*10**15gm/cc as they are supposed to contain one solar mass per ball of 20km diameter!
Still one takes the core at which gravitation collapses to a steady state, it is about 10**12 kg/cc or 10**15 gm/cc, said to be close to the density of a typical nucleus! i.e double that of a neutron star. Compare it with that of the neutron I had estimated to be! 5*10**136 gm/cc (at least).

srini

Critical radius calculation for a material of given density

r(critical) = 2*G*M / c**2 = 2 G * density * (4/3) *pi*r(critical)**3 / c**2;
r(critical) = sqrt(3*c**2/(8*G*pi*density) )= sqrt(2.7*10**16/(8*6.67*10**-11*3.14*density))
With density=1000kg/m**3 for water, r(critical) for water = 4*10**12m approx = 4*10**9km.
Now, it follows that given a value for the material density but assuming homogeneity, the critical value of radius at which the material in spherical form just becomes a blackhole. Further, the critical radius for any other material can be uniquely determined given its specific gravity, i.e. how much heavier than water it is. Taking the average value of specific gravity for our Earth as 5.5, the critical radius would then become 4*10**9 / sqrt(5.5) km = 1.7 * 10**9 km (approx).
In essence, the r(critical) varies with specific gravity in an inverse square root fashion.
With 11.6 for lead, r(critical) becomes about 1.2*10**9 km.

srini

SEARCH FOR EXTRA-TERRESTRIAL LIFE THROUGH RADIO, TV SIGNALS!

Astronomers plan to search 1000 nearby stars for television broadcasts and other signals that could indicate extra-terrestrial life, the Harvard­-Smithsonian center said. The project planned for early 2008, would use a new radio telescope to search for radio traffic similar to that found on the Earth. Current efforts to find extra-terrestrial life look towards messages deliberately beamed across space – an approach that would miss any civilisation that does not advertise its existence as the Earth does. The new effort would search a portion of the electromagnetic spectrum used on the Earth for more mundane purposes – radar, television and FM radio broadcasts. It was hoped that spurious signals from people but not meant for us would be picked up according to the director of communications at the centre.

srini

COSMIC REVELATION

Astronomers unveil detailed 3-D map of universe

A team of astronomers has unveiled a three-dimensional map that sheds light on the mysterious dark matter that makes up a quarter of the universe. The map shows that the dark matter forms a filamentous skeleton upon which visible matter congregates, eventually producing stars, Nature magazine has reported. The composition of the dark matter is unclear but it is believed that without it the universe could not exist. The dark matter is thought to act as glue, holding galaxies together. ‘This is the first time that such a large scale three-dimensional picture of dark matter has been produced, and it will allow cosmologists to probe deeper into the nature of this elusive matter”, the report said.

The map also has a few puzzles within it. Some areas show clumps of dark matter that aren’t accompanied by the bright features associated with conventional visible material (made of Baryonic matter) and vice versa.

“On the large scale, the general picture is as expected, but there are some small-scale discrepancies”, it was reported, based on the map synthesized from hundreds of slightly overlapping images from the Hubble space telescope’s cosmic evolution survey.

“The existence of large clumps of isolated dark matter and visible matter flies in the face of everything we know”, according to a cosmologist from the University of Durham, U.K.

srini

Supernova remnant RCW86 – Dating modified to AD 185

According to a recent study, the supernova remnant RCW 86 is much younger than previously thought, pointing towards a modified date of about AD 185. The formation of the remnant appears to coincide with a supernova observed by Chinese astronomers in AD 185. The study used data from NASA’s Chandra X-ray observatory and the European space agency’s XMM-Newton observatory. Previous suggestions to this effect have been confirmed by the new X-ray data, the lead author reported.

When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.

In the stellar work, the debris in RCW 86 was studied to estimate when its progenitor star originally exploded. It was also calculated how quickly the shocked or energized shell is moving in RCW 86, by studying one part of the remnant. Combining this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand, led to the estimation of the age of RCW 86 afresh – as about 2000 years old.

The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In AD 185, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with the modern observations of supernovas. However, uncertainties about the age provided significant doubt about the association.

The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found that most of the X-ray emission was caused by high energy electrons moving through a magnetic field. This is well known process that gives rise to low energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted. The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.

srini

Coming to density calculation!

If the radius of the neutron has just the critical value of 2x10**-54m (i.e. just a blackhole), the density becomes = 1.67x10**-27kg / ((4/3) 3.14 (2x10**-54m)**3) = 5x10**133 kg/m**3= 5x10**136 g/cc; i.e. a specific gravity of 5x10**136 (so many times heavier than water!).
If any other material cosisting of neutrons, protons, electrons and empty space could become a blackhole for a particular value of radius, the neutron could then be MUCH HEAVIER than as calculated above, especially if the empty space is of orders higher than the dimension of the neutron itself - oops! Now, shall we explore the above 'if', i.e. any other material can become a blackhole?
Let's have a break and meet soon!
srini

My little neutron!

Continuing the calculations, putting the neutron mass as 1.67x10**-27kg, G=6.67x10**-11 and
c=3x10**8m/sec, the radius of the neutron for it be just a black hole needs to be just about 2x10**-54 metre or 2x10**-51 mm. Taking the diametre to be twice the radius, this gives about 2.5x10**50 neutrons stackable in a millimetre! In case the real blackholes contain empty space, the neutron could be much smaller!

srini

Eureka! Eureka! Scientists discover new element - UNUNOCTIUM!

Just as the deliberation is going on about the densest material, there is some news (October 2006) that US and Russian scientists announced that they had discovered a superheavy element, known as 118, albeit one that has only existed in three different atoms lasting a fraction of a second over months of experiments. The last discovery of a naturally occurring element on the periodic table was in 1925 and have since sought to create new heavier elements. The last new elements discovered , 113 and 115, were announced in 2004.

Scientists said they found their first superheavy element 118 atom in 2002, then found another two atoms in 2005 in a second round of experiments in which they fired 10 to the power of 19 calcium ions at the californium. In the end the atoms of element 118 - also known as ununoctium - lasted 0.9 milliseconds, researchers said. But due to some controversies, this was not fully accepted. Adding a fresh lease of hope, in the latest experiments, scientists at the Lawrence Livermore National Laboratory in California and the Joint Institute for Nuclear Research in Dubna, Russia, bombarded Californium with Calcium ions to create 118 - the heaviest ever created in such experiments. 118 denotes the number of protons in the nucleus or the atomic number, technically speaking. It is said to fit just below Radon in the column of the periodic table containing what are called noble gases for their inert chemical properties.

Now the point I (the author of the blog) would like to add and highlight is that the solid form of the element 118 must be considered and that too at absolute zero temperature! I have an inkling that any material cooled to absolute zero could degenerate into a totally packed bunch of neutrons. Am I right? Any comments from our esteemed physicist-fratenity?

srini.
9 nov 2006