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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More on Interstellar Time and Distance

Maybe you’re feeling fed up with the economy, being out of work for two years, global warming, a dysfunctional congress, the UK rioting, and the current political campaign lineups. Are you thinking it’s nearly time for mankind to journey to the stars for a fresh start? It doesn’t look like we’re quite ready for prime time.

I updated my time and distance spreadsheet on my November 10, 2010 Astronomy posting “Interstellar Time and Distance.” This came about thanks to a reader question about distances and times from the Orion Nebula (M42). That calculation has enough steps that I fluffed them on my PC calculator. So I redid the spreadsheet, adding Neptune and Orion M42 to the range. For good measure, and comparison of the vast difference between interstellar and intergalactic travel distances, I also added the Andromeda Galaxy (M31).

If Pioneer kept chugging along at 132,000 miles per hour to the nearest star, Alpha Centauri, it wouldn’t get there for almost 30,000 years. Scientists think we may attain higher speeds around 0.1% of the speed of light within the next century. This might enable future space travelers to get to the Orion Nebula in only 1.2 million years. Better stick to Alpha Centauri at 3,900 years, which will be do-able, though at enormous energy, construction and human cost.

If a colonization team left now for Alpha Centauri, and another left in year 2111, the second team would probably arrive about 26,000 years before the slower first team!

But you’re thinking, “we’ll have Star Wars technology by then.” Unless we discover real live Wormholes and figure out how to survive that transit and predict the destination, travel at even 10% of the speed of light would get us to Alpha Centauri in about 42 years. That would be nice, but it’s still pure science fiction.

Light from our closest galactic neighbor, Andromeda Galaxy, takes 2.5 million years to get here. There’s absolutely no use in even speculating: we’d need at least 25 million years travel time to get there!

Best we just spread more marmalade on the breakfast toast and ponder how we’ll get through the 2012 elections …

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Interstellar Time & Distance

In this Sunday’s comic strip “Beetle Bailey”, the dumbest guy in Camp Swampy asks the smartest questions, and nobody knows the answers. Zero: “Boy! I’d like to visit one of those stars.” Sarge: “It would take you years to travel through space to get to one of them.” Exactly. But how long would that really take?

Beetle Bailey by Mort Walker
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National Geo: Seeking new earths

rocket launch - from National Geographic

rocket launch - from National Geographic

There’s an article of interest in the December 2009 National Geographic, “Worlds Apart: Seeking new earths”. Written for National Geographic by stargazer Timothy Ferris, the article discusses, in lay editorial style, the mission of NASA spacecraft Kepler (the launch image on this page).

Also discussed with excellent graphics is a foldout showing new planets that have been found so far. The newsprint magazine also presents thumbnail concepts of current detection techniques, including subtle changes in parent star luminosity, and doppler wobble.

For those of us who don’t have access to the current old-fashioned subscription magazine (which I prefer), here are current links to the National Geo articles:

The chart covers the 373 found planets (as of when the issue went to press). I didn’t realize we had identified orbiting planets out to 10,000 light years distance. At least one “planet” is really a failed star (17 times Jupiter’s mass) – it should have gone thermonuclear.

Since Andromeda is our nearest neighboring galaxy, some 2.5 million light years distant, the article doesn’t report any discoveries there, and most likely none have been observed. For ET hunters it might be somewhat unsettling to realize that there is no way Earth could be seen from Andromeda with what we consider state of the art technology. Newly launched Kepler will peer out 15 times farther than current sightings, that is, 6,000 lights years distance, as opposed to the current 400.

In that case, where exactly are the host stars for our 373 observations to date? They seem to all be in own Orion Spur of the Milky Way’s  Sagittarius arm. Even Kepler is confining its search area to this spur.

For the seasoned amateur astronomer, there is perhaps not much content we haven’t read elsewhere, at some time or other,  in astronomy magazines and websites. But the National Geo presentation is well-organized, as generations have come to expect from that publication, and well worth our review.

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Scaling the Solar System

Credits: click link in picture

What would the solar system “look like” if we could scale it down to walking distances?

Most of us have seen diagrams such as the classroom picture above, showing the relative size of the planets. Note that they can never get more than a small arc of the entire Sun’s orb in these pictures. If all of the objects were spaced out proportionally, at this scale how big would the Sun appear? How far away would Earth and all the planets be?

This exercise isn’t just for students. I knew the Sun was about 93 million miles away. I knew the Earth was about 8,000 miles in diameter. But I was stupefied to learn the Sun is the better part of a million miles in diameter: 864,936 miles is the published figure I found.
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