Will Earth Perish by Fire, Ice or Black Hole?

On last night’s news, veteran PBS news anchor Gwen Ifill interviewed a prominent astronomer to solicit comment on the recent discovery of two enormous black holes hiding in the bright central bulges of the giant elliptical galaxies NGC 3842 and NGC 4889.

The scientific news itself went “viral,” being picked up on BBC, The New York Times, Huffington and elsewhere that I can recall, as well as in the scientific journals. The Sky & Telescope article is much more oriented toward readers who are already familiar with cosmological objects and distances. It can be picked up at this link.

You can also read the PBS transcript of Ifill’s interview with Chung-Pei Ma. Ma is professor of astronomy at the University of California, Berkeley. She appeared visibly constrained by the problem of how to explain these concepts to a general viewing television audience.

But the item here concerns Gwen’s question to Chung-Pei Ma. Presumably Gwen had done her homework and knew the answer, but most viewers might not:

[quote]GWEN IFILL: Nearby, but not a threat? I mean, we’re not — you’re talking about black holes that suck in light and gases and everything in its path, but we’re not in its path?”[/quote]

Ma tried to explain, in lay terms, why not. Breaking this question apart, the salient components of a better answer would be:

  • how far out do the effects of these monster black holes reach?
  • how far away are we now?
  • how long in years could an approach to within their spheres of gravitational influence take?

Facts:

  • Both galaxies in question are about 300 million light years away.
  • “For NGC 3842’s central monster, the team found a mass between 7 and 13 billion Suns; for NGC 4889 the range is much bigger: 6 to 37 billion solar masses” [Sky & Telescope].
  •  In other words, each black hole’s estimated bulk suggested it had already swallowed the mass equivalent of an entire “ordinary” galaxy.
  • The “event horizon” of each black hole – the boundary inside of which even light cannot escape the black hole’s unimaginable gravitational field – is estimated at around 3 to 5 solar system diameters.
  • Our Solar System has a diameter of about 0.001 light year. To put this into some kind of perspective, our Milky Way galaxy has a diameter of about 100,000 light years.

Discussion:

  • So, our Milky Way (which has a large black hole of its own) is about 3,000 Milky Way diameters away from NGC 3842 and NGC 4889.
  • Looking at the second illustration in the Sky & Telescope article, and the companion text, it appears that only the the motion of stars within 1,000 light years of their black holes NGC 3842 and NGC 4889 are affected by the nearby dark monsters.
  • We are 300,000 times further way than that.

Devil’s Advocate:

But … but … supposing some cataclysmic upheaval were to propel our solar system, or our planet, toward those monster black holes? How long might it take for them to tear us apart? How fast could an “object” like us move in that direction?

Obviously, we’d have to move really fast.

  • Let’s disregard the fact that any catastrophic event powerful enough to do that would also undoubtedly shred Earth to dust, if not elemental gases.
  • A supernova explosion of our Sun might propel an expanding sphere of gases and dust outward at 11 million miles an hour, though it’s a fact our Sun is way too small to go supernova.
  • According to a Stanford article  “THE MYSTERY OF THE FASTEST MOVING STAR STILL PUZZLING,” they mention a candidate speed in this question: “How do you accelerate 2.7 octillion tons (27 followed by 26 zeros) from a standstill to over 1,800 kilometers per second, about one- half of one percent of the speed of light? That could be as fast as 4 million miles per hour.”

So, even at the catastrophic speed of one percent of the speed of light (give or take), hurtling straight toward either of those two monster black holes, it would take us something like 30,000 million years to reach a destination 300 million light years distant. The universe is currently 13.7 billion years old. Cosmologists think it might be good for another 10 or 20 billion years or so before perishing in fire, or ice, or whatever.

In short: since 30,000 million years is 30 billion years, the universe may not even exist by the time a battered Earth arrives at NGC 3842 and NGC 4889 at the improbably high speed of only one percent of the speed of light. Any slower than that, we’d never arrive, nor would there be any destination to arrive to. I don’t think we have to worry about it too much.

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Hubble Directly Images Black Hole Accretion Disk

For the full story see the NASA Hubble site: NASA/ESA managed to combine the powerful Hubble Space Telescope with the incredible sling-shot magnification of gravitational lensing to produce what appears to be mankind’s first visible-light image of an accretion disk. .

 

[quote]An international team of astronomers has used a new technique to study the bright disc of matter surrounding a faraway black hole. Using the NASA/ESA Hubble Space Telescope, combined with the gravitational lensing effect of stars in a distant galaxy [1], the team measured the disc’s size and studied the colours (and hence the temperatures) of different parts of the disc. These observations show a level of precision equivalent to spotting individual grains of sand on the surface of the Moon.[/quote]

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The End of Cosmology

According to the article “The End of Cosmology” in the March Scientific American, “evidence of the universe is disappearing as the universe expands.”

I guess that’s OK, as long as it doesn’t happen before my subscription runs out.

Edwin Hubble figured out not only that the universe is expanding, but that the speed at which an object recedes due to expansion of the universe is proportional to its distance. That is, an object twice as far away is expanding away from us twice as fast.
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Fat Singularities and Skinny Infinities

Foggy Mist

HubbleIMAGINE that it is a really cold morning, and you have taken a REALLY hot shower. Not just the bathroom mirrors are fogged. The bathroom itself is filled with steam. In fact, the living room windows are even fogged over. So we open the sliding glass door for a little while to vent the moisture.

Instantly, or PDQ as near as anyone can tell, the mist expands out of the apartment to uniformly fill your entire hometown.
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Observable Universes and Other Oddities

Recently we mused about the “observable universe“, a 10^28 cm radius patch of real estate centered on us, the observer, where the radius of this fanciful sphere should be equal to the theoretical distance light could have traveled since the Big Bang.

Thinking about it, of course, leads to the conclusion that it all depends on what you mean by “observable”. The web references confirm we only mean that light could have reached us from somewhere, at some point in time since the universe became transparent. “Observable” doesn’t directly guarantee us what we can see, and the entire universe is much bigger; last I heard, no one was speculating that the entire universe is bounded and finite.
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Getting to the Observable Universe

Roll up your sleeves. Some junior high school math with lots of powers of ten is coming up.

After all, honestly, it’s not as if I’d have the good sense to leave well enough alone. In the previous post, we discussed the current size of the “observable universe” (10 to the 28th power centimeters), and cosmology models that depend on “inflation” to explain how we got so big so fast. If, that is, you accept that the 14 billion year age of the universe is “so fast”.

But light travels pretty fast. If the universe only expanded at the speed of light, and (almost by definition, you’d think) has done so ever since the Big Bang 14 billion years ago, that would make a pretty big sphere today. Do we really need “inflation” to account for the 10^28 cm size of today’s “observable universe”?
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Fahrenheit 10^10^12

Periodically one might wonder why Herr Daniel Gabriel Fahrenheit fixed his temperature scale to a freezing point of water at 32 degrees, and the boiling point, at 212 degrees. Reading in Wikipedia that the numerical difference between boiling and freezing is exactly 180 furnishes one with relatively little additional comfort, unless one is planning a series of experiments in which the temperature of ice needs to be raised to boiling in exactly 180 annoying little increments.

For the big numbers of really hot stuff, of course, scientists use the Kelvin scale, so we say the surface of the sun has a temperature of about 8,500 Kelvin, whereas the surface of a white dwarf is closer to 85,000 Kelvin. For true convenience, this can be converted back to Fahrenheit using the formula TF = (TK whatever 459.67 … where we see that for big numbers the 459.67 conversion constant doesn’t mean a damn thing, and 85,000 x 9/5 is plenty close enough for government work.
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Cosmology: Causal Horizons

My?June issue of Sky and Telescope magazine also had an interesting article on the creation and ultimate end of the Solar System. Though details are somewhat speculative, we know that the Sun is about halfway through its Main Sequence, so it will gradually get hotter, with unpleasant consequences for Earth. Toward the end of the main stellar sequence, the Sun will start expanding into a Red Giant, engulfing Mercury, and possibly Venus. Our now-blackened cinder planet will endure some billions of years of this; as the wreckage of Sol contracts into a white dwarf inside the death shroud of an expanding planetary nebula, what is left of everything will cool. Finally, orbitally destabilized Jupiter or Saturn, or possibly a wandering white dwarf, may, by gravitational slingshot, unceremoniously eject our dead Earth out into the deep void, far from its home solar system, wandering for trillions of years in uncharted space.
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More Godless Cosmology

Eagle Nebula - mists of light?The June Sky and Telescope had three interesting letters to the editor. In the March issue, a reader had written to complain that God is consistently left out of cosmological theories. One June letter noted that adding God to the mix just pushes any explanation a step further back, irreverantly asking who then, had created God, and what mechanism did He then use? Another dryly noted that science concerns itself with natural phenomena, not supernatural. He added: “highly speculative” religious theories need only be internally consistent – they can ignore scientific factfinding and advances, needing only not to contradict other parts of their religious teachings. The third writer asks why we can’t expect our scientists to base their theories on the evidence, just as we expect from doctors, lawyers, reporters and your local auto mechanic.
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Sloan Digital Sky Survey: You are Here

This Sloan Digital Sky Survey map of the universe is 2 billion light-years deep. Each point represents a galaxy with a measured redshift. Maps like this have revealed the signature of enormous sound waves rippling through the early universe. Courtesy Sloan Digital Sky Survey.

(text and picture from Sky and Telescope, January 12, 2005)

You are here. Approximate scale 1″ = 1 billion light years. Map may not be suitable for navigational purposes. Objects may be further away than they appear.

Sloan Digital Sky Survey

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