Mystery deepens over origin of biggest black holes

Mysteries are popular, so heres a good one, about another popular subject, black holes.

Mystery deepens over origin of biggest black holes (5/19/08)

Where did the universes biggest black holes come from? One idea suggests the behemoths began as smaller "seed" black holes that gobbled up surrounding gas. But new computer simulations suggest these seeds were born with practically nothing around them to eat, deepening the puzzle over how the biggest black holes came to be. ...

How these supermassive black holes grew so big so fast has been a major puzzle. Some astronomers have suggested that they grew from smaller black holes of about 100 times the Suns mass, left behind when the universes first stars collapsed at the end of their lives.

Note that this isnt the only way that black holes could have formed, not even black holes of about this size. Thats good, because what this study seems to show is that it would be difficult for a black hole formed from a collapsed early star to accrete enough matter to grow into a supermassive black hole (SBH).

But the universes first stars were not born until a few hundred million years after the big bang. Even though they lived only a few million years before collapsing to form black holes, this does not leave much time for these seeds to grow into the monstrous black holes powering quasars.

The puzzle now appears to have deepened, with new computer simulations suggesting that these seed black holes were born with little food around them from which to gain weight.

Tom Abel of Stanford University in California, US, and his colleagues made computer models simulating the first generation of stars. These first stars are thought to have been very massive and luminous, weighing about 300 times as much as the Sun. The simulations reveal that the stars prodigious radiation would have blown away the gas around them.
Early famine

As a result, the black holes that formed when the stars died a few million years later would have had very little to eat. In the simulations, it took about 100 million years for the gas to fall back towards the first black holes and provide them with something to eat. The time lost due to the early famine makes it even harder to imagine how these black holes could have swelled to billions of times the Suns mass soon thereafter.

Lets just suppose this simulation result makes the formation of SBHs from such seeds very unlikely. Are there other reasonable possibilities?

Sure there are. One is that black holes dont exist at all, so neither do SBHs. Never mind that most galaxies seem to contain very massive objects, whose mass is 10⁵ solar masses or more. (Normally written as 10⁵M_⊙.) The Milky Way itself has a black hole at its center, whose mass is estimated at 3.7×10⁶M_⊙.

Such massive objects need an explanation too, which would have at least the same difficulties as for SBHs. But weve already noted that the evidence for black holes is very solid (see here), so lets rule this out.

Heres another recent hypothesis:

Biggest black holes may grow inside quasistars (11/29/07)

The biggest black holes in the universe might have grown within the bellies of giant stars, a new study suggests. If these hole-bearing "quasistars" exist, then they might be bright enough to see from across the universe.

Quasistars are one attempt to explain the existence of supermassive black holes, which astronomers have detected at the hearts of most large galaxies, and whose origin is still unknown.

It is calculated that this could account for objects up to 10⁴M_⊙ in size. One problem here is that possible quasistars have never actually been observed, and observation is expected to be difficult at best, since they would have formed so soon after the big bang, and consequently now be very distant (like more than 10¹⁰ light-years).

Another problem is that SBHs can be far larger than this. The largest SBH known so far is about 1.8×10¹⁰M_⊙. (See here, here.) SBHs that formed in quasistars would still need to accrete something like 10⁶ times their initial mass to grow into the largest known SBH, let alone any larger ones that might be out there. (For comparison, the mass of the Milky Way, a medium-size galaxy, is about 10¹²M_⊙. See here, here.)

So a quasistar origin for SBHs doesnt seem too likely either, but if you want to pursue it further, the relevant paper is here.

We havent yet even mentioned one obvious possibility: primordial black holes (PBHs). That is, black holes that formed directly very soon after the big bang itself. Exactly at what time this might have been depends very much on how PBHs might have formed, and theres plenty of uncertainty about that.

In fact, we have no evidence yet that PBHs exist at all. Since we dont know exactly how they might have formed, we dont know how big they might be, which strongly affects what we should look for. If PBHs were small enough, they should eventually "evaporate", as Stephen Hawking suggested, by the process of Hawking radiation.

Theres much debate as to what happens when a sufficiently small PBH evaporates completely (see here, here, here, here, here). But such an event is generally supposed to include emission of gamma-rays, and these might be detected by the newly-launched GLAST mission. (See here.)

The most likely scenario for the formation of a PBH is as a result of gravitational collapse of overdense regions existing because of density fluctuations dating from the earliest instants after the big bang. Since fluctuations are the key, formation of PBHs is governed by probability, and the larger the PBH, the lower its probability, and hence the fewer that form altogether. While theres no obvious upper limit to the size of a PBH, the formation of one around 10⁴M_⊙ would be very improbable. Too improbable? No one knows.

Other mechanisms hypothesized for formation of PBHs tend to feature rather exotic things like topological defects (cosmic strings or domain walls) or certain kinds of phase transitions.

But this is all so speculative that its not much help for evaluating whether PBHs might make a good source of SBHs. A great reference for stuff about PBHs is this: Primordial Black Holes: Do They Exist and Are They Useful?.

The bottom line is that closer study of SBHs, which almost certainly do exist, should eventually lead us to some concrete evidence for things that are presently much more speculative.

Tag: black holes, supermassive black holes, primordial black holes

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What If the Biggest Solar Storm on Record Happened Today

National Geographic has an article on the possible impact of a large scale solar eruption of the order of 1859s "Carrington Event" - What If the Biggest Solar Storm on Record Happened Today?.

On February 14 the sun erupted with the largest solar flare seen in four years—big enough to interfere with radio communications and GPS signals for airplanes on long-distance flights.

As solar storms go, the Valentines Day flare was actually modest. But the burst of activity is only the start of the upcoming solar maximum, due to peak in the next couple of years.

"The sun has an activity cycle, much like hurricane season," Tom Bogdan, director of the Space Weather Prediction Center in Boulder, Colorado, said earlier this month at a meeting of the American Association for the Advancement of Science in Washington, D.C.

"Its been hibernating for four or five years, not doing much of anything." Now the sun is waking up, and even though the upcoming solar maximum may see a record low in the overall amount of activity, the individual events could be very powerful.

In fact, the biggest solar storm on record happened in 1859, during a solar maximum about the same size as the one were entering, according to NASA.

That storm has been dubbed the Carrington Event, after British astronomer Richard Carrington, who witnessed the megaflare and was the first to realize the link between activity on the sun and geomagnetic disturbances on Earth.

During the Carrington Event, northern lights were reported as far south as Cuba and Honolulu, while southern lights were seen as far north as Santiago, Chile. (See pictures of auroras generated by the Valentines Day solar flare.)

The flares were so powerful that "people in the northeastern U.S. could read newspaper print just from the light of the aurora," Daniel Baker, of the University of Colorados Laboratory for Atmospheric and Space Physics, said at a geophysics meeting last December.

In addition, the geomagnetic disturbances were strong enough that U.S. telegraph operators reported sparks leaping from their equipment—some bad enough to set fires, said Ed Cliver, a space physicist at the U.S. Air Force Research Laboratory in Bedford, Massachusetts.

In 1859, such reports were mostly curiosities. But if something similar happened today, the worlds high-tech infrastructure could grind to a halt.

"Whats at stake," the Space Weather Prediction Centers Bogdan said, "are the advanced technologies that underlie virtually every aspect of our lives."

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Canberra grants pave way for world’s biggest wave turbine

Giles Parkinson at ReNewEconomy has an article on the release of some government funding to wave power companies BioPower (mentioned in this post on biomimicry) and long time developer OceanLinx to build pilot plants (following an earlier funding round to Carnegie Corp in WA) - Canberra grants pave way for world’s biggest wave turbine.

The Australian government as upped its investment in two nascent, Australian-developed wave energy technologies, announcing new grants worth almost $10 million to help bring the two new systems to the market, including what is believed to be the world’s biggest wave energy turbine.

The government is providing $5.6 million to BioPower Systems to install a 250kW full-scale pilot plant of its bioWAVE technology off the coast of Victoria, and is also providing just under $4 million to Oceanlinx, to install a 1MW demonstration plan of its Greenwave technology in South Australia.

Both grants are being made under the $126 million Emerging Renewables program, and follow an earlier $9 million grant to Carnegie Wave Energy, which is building a $31 million, 2MW grid-connected demonstration of its CETO technology near Fremantle in Western Australia.

BioPower CEO Tim Finnigan said the grant, along with a $5 million grant from the Victorian state government, means that its $15 million project was now fully funded. “This puts us into a position to complete the project, get it on the grid, and prove the technology at scale,” he told RenewEconomy. “It’s a pretty big development for us.”

The technology is best described with an image, see below. It’s designed to lay flat on the ocean floor when the waves become too big (it calculated this to be around 1 per cent of the time).

It is designed to absorb energy both at the surface and below. It is mounted on sea-floor, the demonstrator will be in about 30m of water, and the array of buoyant floats, sways back-and-forth in tune with the waves, and the energy contained in this motion is converted to electricity by an onboard self-contained power conversion module, and is delivered through a cable.

However, the first demonstration plan will weigh 400 tonnes when it is installed at a site 4kms from Port Fairy on the southern coast of Victoria. “We not trying to prove a light-weight structure right now,” Finnigan says. “We will carve our way to that over time.”

Like Carnegie Energy, Finnigan says the long term goal for wave energy has to be to match wind – which means capital costs of around $2 million/megawatt and a levellised cost of energy at $100/MWh or below. He says BioPower has a four-stage plan to reach that target by the end of the decade. ...

Meanwhile, Oceanlinx says it believes its GreenWave device (see below) is the first in the world to be rated at 1MW, and its efficiency has improved 50 per cent since an earlier, smaller version that was deployed near Port Kembla in NSW. The 20m by 20m structure, around 17m high, will sit in around 10m of water. It features an oscillating water column, with the turbine and other moving parts above the waterline. The 2,000 tonne concrete structure will sit on the ocean floor.

CEO Ali Baghaei says this demonstration unit will have an LCOE of 28c/kWh, which will fall to 16c/kWh once 5MW have been installed and to below 10c/kWh once 75MW have been installed. The initial project will cost $7.2 million, with the balance coming from a recent $8 million fund raising from existing investors. ...

Resources and Energy Minister Martin Ferguson said the grants made Australia “one of the world’s largest supporters” of wave energy technology. “Wave energy is still very much an emerging technology and this funding will position Australia as a global leader in developing this technology,” he said in a statement, adding that wave energy had the potential of providing 1300 terawatt hours per year, or about five times Australia’s total electricity requirements.

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