Starship Asterisk*

Hi

I found this.

http://www.nature.com/nature/journal/v3 ... 614a0.html

http://www.msnbc.msn.com/id/34436949/ns ... nce-space/

I must ask, What else have they seen through, absorption and diffraction of interstellar dust, And got the numbers wrong?

Regards

Mark

mark swain wrote: http://www.nature.com/nature/journal/v3 ... 614a0.html
http://www.msnbc.msn.com/id/34436949/ns ... nce-space/

I must ask, What else have they seen through, absorption and diffraction of interstellar dust, And got the numbers wrong?

Just about everything is seen through the absorption of interstellar dust which is always somewhat tricky to estimate.

http://antwrp.gsfc.nasa.gov/apod/ap970115.html

http://blackholes.stardate.org/directory/factsheet.php?p=V404-Cygni wrote:
<<V404 Cygni has something of an identity crisis. The "V" in its name indicates that it is a variable star, so it gets brighter and fainter. It's also known as a nova, because at least three times in the 20th century it produced a bright outburst of energy. Finally, it's known as a soft X-ray transient because it periodically emits short bursts of X-rays.

Together, these identities tell astronomers that V404 Cygni is a binary system that consists of a black hole and a "normal" companion star, and that the black hole is stealing hot gas from the companion. The flow of gas between stars isn't even, though, so the system produces occasional "flickers." And when enough gas builds up in a disk around the black hole, there is a much larger outburst that can cause the system to shine hundreds of times brighter than normal.

V404 Cygni's black hole is one of the most solid cases of a stellar-mass black hole in the galaxy. Several careful studies of how the two stars orbit each other show that the "dark" member of the system is probably around 12 times as massive as the Sun. Only a black hole could be that small and heavy. The companion star is about two-thirds as massive as the Sun. Its surface is cooler, so it shines yellow-orange.

The two stars orbit each other once every 6.5 days, which indicates that they are quite close together. At that range, the black hole's powerful gravity causes the companion to bulge toward it, so the star is egg-shaped. Gas flows from the "point" of the egg toward the black hole. Most of the time, this flow is fairly thin but steady, although it's clumpy enough that the entire system can appear to flicker a little, which is one reason why it's designated as a variable star.



An artist’s concept of a microquasar, like V404 Cygni. The black hole is stealing gas from a companion star (left). The gas forms a thin, hot disk around the black hole. When enough gas builds up there is a bright flare-up of X-rays, and jets of charged particles squirt away at close to the speed of light.

Gas slowly creates a disk around the black hole, known as an accretion disk. The gas in this disk produces energy, too, adding to the total brightness of the system. However, the disk isn't as bright as a disk around a neutron star. That's because in a neutron-star system, the gas remains visible as it spirals onto the surface of the star. It heats up as it gets closer to the neutron star's surface, so it shines brighter. In a black hole system, though, the gas is swallowed as it crosses the black hole's event horizon, so the system can't shine as brightly.

The process of transferring gas from one star to the other isn't completely smooth, though. There can be "lumps" in the stream, or in the disk around the black hole. These lumps create flares of X-rays that are easily detected by X-ray satellites in space -- hence the label "soft X-ray transient" ("soft" refers to the frequency of the X-rays). The X-rays also light up the gas between the two stars, making the system shine even brighter.

The gas continues to build up around the black hole until it reaches a critical density. The gas then quickly heats up, making the accretion disk shine brighter. Gas in the inner portion of the disk suddenly plunges into the black hole; in the moment before it crosses the event horizon, it shines brightest of all. This "big gulp" produces an outburst of energy not just in X-rays, but in all wavelengths. The system can shine hundreds or thousands of times brighter than normal -- hence the label "nova."

V404 Cygni first jumped to prominence during a nova eruption in 1938. It produced eruption in 1989, which was discovered by an orbiting X-ray satellite and confirmed by telescopes on the ground. The system grew about 200 times brighter in visible wavelengths, and much more than that in X-rays. The system is likely building toward another eruption, although so far, astronomers don't know when to expect it.>>

Well, This just blew me away. lost for words. Enjoy.

tc

I used to be terrified of black holes, but now I'm pretty bored, actually.

So the black hole of V404 Cyg may have a mass of twelve stars like our Sun. And it may be 7000-8000 light years distant. Fascinating, but dangerous? C'mon. If the Sun, which admittedly "only" weighs one solar mass, but is, on the other hand, only eight light minutes away from us - if our Sun doesn't eat us up, why would the black hole of V404 Cyg do it?

All right, I guess that V404 Cyg might still kill us, just possibly. It might swallow a huge helping of gas from its hapless companion and burp out a tremendous jet straight in our direction. How likely is that, however? Seems the chances of such a jet missing us rather than hitting us are pretty overwhelming.

Also, I guess the black hole could swallow the entire poor fellow of a star orbiting it in one fell swope or mouthful, and that would certainly give our stellar singularity a lot of indigestion and cause some really bad black hole behaviour. Yes, yes, that could happen, and it could happen in our lifetime, and a flowerpot may fall from a window six floors above and hit you on the head and kill you. And California may have that monster earthquake that may cause the Arnold Schwarzenegger-governed state to topple straight into the Pacific Ocean, which is what everyone has been worrying about when they remember to worry about it. And some weeks ago we had a really big thunderstorm here in Sweden, and I was sitting on the patio under a roof where there was a bolt of lightning and a crack of thunder at virtually the same time. Wow.

So... am I worried about V404 Cyg? You must be kidding.

Ann

Ann wrote:
I used to be terrified of black holes, but now I'm pretty bored, actually.

... So... am I worried about V404 Cyg? You must be kidding.

You've obviously never seen a naked singularity in the flesh before

http://en.wikipedia.org/wiki/Naked_singularity wrote:
<<In general relativity, a naked singularity is a gravitational singularity without an event horizon. There is a region around a singularity, the event horizon, where the gravitational force of the singularity is strong enough so that light cannot escape. Hence, the singularity cannot be directly observed. A naked singularity, by contrast, is observable from the outside. The theoretical existence of naked singularities is important because their existence would mean that it would be possible to observe the collapse of an object to infinite density. It would also cause foundational problems for general relativity, because in the presence of a naked singularity, general relativity cannot make predictions about the future evolution of spacetime.

Some research has suggested that if loop quantum gravity is correct, then naked singularities could exist in nature, implying that the cosmic censorship hypothesis does not hold. To this date, no naked singularities have been observed.>>

Ann wrote:All right, I guess that V404 Cyg might still kill us, just possibly. It might swallow a huge helping of gas from its hapless companion and burp out a tremendous jet straight in our direction. How likely is that, however? Seems the chances of such a jet missing us rather than hitting us are pretty overwhelming.

At 8000 ly, even that poses no risk with such a low mass object.

You're right, black holes are not very scary. Those who find them so have probably seen too many bad science fiction movies.

Art said:

You've obviously never seen a naked singularity in the flesh before

How indecent!!!! Now I think I'm a nervous wreck! Isn't there a brave politician who will start a crusade against black hole nymphomania?

Ann

Chris Peterson wrote:
You're right, black holes are not very scary.

Those who find them so have probably seen too many bad science fiction movies.

Yellow Solaranite...NOW THAT'S SCARY

http://www.imdb.com/title/tt0052077/quotes wrote:
[list]Quotes for _Plan 9 from Outer Space_ (1959) [/list]Criswell: Greetings, my friend. We are all interested in the future, for that is where you and I are going to spend the rest of our lives. And remember my friend, future events such as these will affect you in the future. You are interested in the unknown... the mysterious. The unexplainable. That is why you are here. And now, for the first time, we are bringing to you, the full story of what happened on that fateful day. We are bringing you all the evidence, based only on the secret testimony, of the miserable souls, who survived this terrifying ordeal. The incidents, the places. My friend, we cannot keep this a secret any longer. Let us punish the guilty. Let us reward the innocent. My friend, can your heart stand the shocking facts of grave robbers from outer space?
.....................................
Colonel Tom Edwards: You speak of Solaranite. But just what is it?

Eros: Take a can of your gasoline. Say this can of gasoline is the sun. Now, you spread a thin line of it to a ball, representing the earth. Now, the gasoline represents the sunlight, the sun particles. Here we saturate the ball with the gasoline, the sunlight. Then we put a flame to the ball. The flame will speedily travel around the earth, back along the line of gasoline to the can, or the sun itself. It will explode this source and spread to every place that gasoline, our sunlight, touches. Explode the sunlight here, gentlemen, you explode the universe. Explode the sunlight here and a chain reaction will occur direct to the sun itself and to all the planets that sunlight touches, to every planet in the universe. This is why you must be stopped. This is why any means must be used to stop you. In a friendly manner or as (it seems) you want it.

Lieutenant John Harper: He's mad.

Tanna: Mad? Is it mad that you destroy other people to save yourselves? You have done this. Is it mad that one country must destroy another to save themselves? You have also done this. How then is it "mad" that one planet must destroy another who threatens the very existence-...

Eros: [shoves Tanna roughly aside] That's enough.

Eros: [to the humans] In my land, women are for advancing the race, not for fighting man's battles.

Ann wrote:So... am I worried about V404 Cyg? You must be kidding.

How many of those harmless black holes, are wondering around the milky way? 200 billion stars, times 13 billion years. There Must be one or two of them. Good job we'll not see em coming Huh?

tc

swainy wrote:

Ann wrote:So... am I worried about V404 Cyg? You must be kidding.

How many of those harmless black holes, are wondering around the milky way?

They wonder as they wander out under the sky...

swainy wrote:There Must be one or two of them. Good job we'll not see em coming Huh?

Or will we?

http://en.wikipedia.org/wiki/Gravitational_microlensing wrote:
<<Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects ranging from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit lots of light (stars) or large objects that block background light (clouds of gas and dust). These objects make up only a tiny fraction of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.

When a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Einstein in 1915, leads to two distorted unresolved images resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background 'source' and the foreground 'lens' object.

Since microlensing observations do not rely on radiation received from the lens object, this effect therefore allows astronomers to study massive objects no matter how faint. It is thus an ideal technique to study the galactic population of such faint or dark objects as brown dwarfs, red dwarfs, planets, white dwarfs, neutron stars, black holes, and Massive Compact Halo Objects. Moreover, the microlensing effect is wavelength-independent, allowing to study source objects that emit any kind of electromagnetic radiation.

Microlensing by an isolated object was first detected in 1993. Since then, microlensing has been used to constrain the nature of the dark matter, detect extrasolar planets, study limb darkening in distant stars, constrain the binary star population, and constrain the structure of the Milky Way's disk. Microlensing has also been proposed as a means to find dark objects like brown dwarfs and black holes, study starspots, measure stellar rotation, look for cosmic strings, study globular clusters, and probe quasars, including their accretion disks.>>

I seem to remember that a probable black hole was found some years ago thanks to microlensing. It was a small, free-floating black hole, just the kind that Swainy was talking about. So yes, I'm convinced that such invisible lonely black holes exist. It would most definitely not be a good thing if such an isolated black hole came floating into our solar system.

But what are the chances that it will? Some years ago I made a model of the inner solar system. I used a round yellow table cloth, two meters in diameter, for the Sun. (Well, I had to make it yellow, otherwise I couldn't show my model to other people and make them understand that the table cloth was the Sun, could I?)

I used small peas for Mercury and the Moon and somewhat larger cotton balls, two centimeters in diameter, for Venus, the Earth and Mars. (Yes, I know that the Mars cotton ball ought to have been smaller, but I had to approximate.) Venus was a white cotton ball, the Earth a blue cotton ball and Mars a red cotton ball.

Now I had to place these objects at the proper distance from each other. I don't remember how far away from the "Sun" that I put Mercury and Venus, but I remember that I had figured their proper distances out, more or less. I do remember that I put the Earth at two hundred meters from the "Sun", and Mars at three hundred meters away from it. Again, this was of course an approximation, but it was good enough for my purposes. As for the Earth and the Moon, I think I held them about sixty centimeters away from each other.

Well, I ended up with an inner solar system that was absolutely shockingly empty. I had two persons holding up the "Sun" for me. I then walked away from the "Sun" with a group of people who wanted to see where I would place the planets. Taking meter-long strides (more or less), I determined when the person holding up "Mercury" would have to stop. Everybody stopped and looked back at the "Sun". So this is how big the Sun would look in the sky from the vantage point of Mercury, then? After we had put "Mercury" in its proper "orbit", we continued walking until I determined that we had reached the postion of "Venus". The "Venus-carrier" remained in her place while the rest of us continued walking until we were two hundred meters from the "Sun", so that we had reached the position of the "Earth". I made sure that the person holding the "Earth" remembered to keep the pea-sized "Moon" about sixty centimeters away from the "Earth" in his other hand.

As we reached the postion of the "Earth", everybody marvelled at how far away we seemed to have walked from the people holding the "Sun". The "Sun" looked so tiny, even though it had looked extremely big when I had shown off the table cloth and the peas and the cotton balls before we started our walk. But everyone agreed that the real Sun looks about this small in the sky when we see it from our vantage point of the Earth.

I left the "Earth-carrier" in his place, while the rest of us walked to the postion of "Mars". Now the Sun looked just ridiculously tiny. As for the Earth, we couldn't see it at all. We could see the person holding the Earth and the Moon, of course, but we couldn't see the "Earth" that he was holding.

This experiment brought home a couple of points. First, although the inner solar system is a comparatively crowded place as cosmic neighbourhoods go, it is still incredibly empty. Second, compared with everything else in space, the Moon is ridiculously close to us. Have you ever doubted that Neil Armstrong and the other Apollo astronauts ever walked on the Moon? Have you ever wondered why the United States didn't follow up its successful Moon landings by sending astronauts to Mars pretty much right away? You can stop wondering and doubting right now. Do you realize that Mars is approximately 150 times farther away from us than the Moon? Imagine that you taught your son to swim, and you knew he could swim across a hundred meter pond. Just because you knew he could swim across that pond, would you be comfortable dropping him in the middle of a ten thousand meter lake and feel certain that he could swim ashore?

The third point that my experiment brought home is that our galaxy must be absolutely incredibly large and empty. After all, compared with the rest of our galaxy, the Solar system, let alone the inner Solar system, is incredibly tiny and crowded. Even so, it is so marvellously large and empty. So how large and empty is our entire galaxy?

Swainy, you said:

How many of those harmless black holes, are wondering around the milky way? 200 billion stars, times 13 billion years. There Must be one or two of them. Good job we'll not see em coming Huh?

If you ask me, there must be many, many more than just one or two lonely and invisible black holes wandering around the Milky Way. If you ask me, there must be thousands of them, maybe tens of thousands of them. Or hundreds of thousands of them? Maybe millions of them? Even more of them? No. I don't think there are more than a million of them. In fact, I really doubt that there are that many. But there are undoubtedly some of them out there.

Okay. And so what? There are two hundred billion stars in our galaxy. If a perfectly normal ordinary star came blundering into our solar system, it might wreak as much havoc here as a black hole would. Suppose that astronomers found a lonely black hole only nine light years away from us. Wouldn't people be terrified? Wouldn't we think that the black hole was immediately headed our way? But Sirius is nine light years away from us. When was the last time you worried that Sirius would come blundering straight into our solar system, its white dwarf companion in tow? If we don't assume that Sirius is trying to do us in, why should we think that an invisible black hole is lurking out there and has got our number?

Given how much empty space our galaxy contains, the chances that one of those free-floating black holes that undoubtedly exist would happen to wander into our own tiny, tiny, tiny, microscopic part of our galaxy is... well, zero. Or one in a quintillion, or one in an umpti-zillion, or something like that. In other words, it is, for all intents and purposes, zero.

Ann

Ann wrote:Okay. And so what? There are two hundred billion stars in our galaxy. If a perfectly normal ordinary star came blundering into our solar system, it might wreak as much havoc here as a black hole would.

That's really the important point. In terms of its effects, there is no difference between a black hole and a star that is still fusing. If anything, the latter would be more devastating because of its energy output. But either way, a stellar mass object passing near the Solar System would disrupt the orbits of all the planets. It would end life on Earth. But as you note, we don't seem to have any stars randomly passing through, so why expect a black hole, when there are surely millions of stars for each black hole?

Unless, an:

Orange Dwarf Star Set to Smash into The Solar System
A new set of star velocity data indicates that Gliese 710 has an 86 percent chance of ploughing into the Solar System within the next 1.5 million years.

http://www.technologyreview.com/blog/arxiv/24917/

Chris Peterson wrote:But as you note, we don't seem to have any stars randomly passing through, so why expect a black hole, when there are surely millions of stars for each black hole?

Quote:
In particular, this data allowed astronomers to work out which stars we'd been closer to in the past and which we will meet in the future. It turns out that 156 stars fall into this category and that the Sun has a close encounter with another star (meaning an approach within 1 parsec) every 2 million years or so.

I guess, we should hope they didn't miss anything.

tc

Wayne wrote:
<<The Sun is more massive than 85% of all other stars. Most stats are dim K and M class red dwarfs (and theory predicts that even they are outnumbered by brown dwarfs ten to one). The average spacing is not 4 lys, it's around 0.1 Msun/pc^3. This works out to a mean distance between stars of around 1.4 ly.

http://asterisk.apod.com/vie ... 28#p118301

The Sun's neighbourhood is quite anomalous (don't read much into this, it was passing through a very dense region just 30 million years ago - The non-avian dinosaurs are over twice as old) in that it contains many massive stars and few normal stars. Related to this, the average spacing is much higher than normal, within 20 light years the average spacing is around 3 ly (counting binaries as one). The Sun itself is on the high side of spacings, but in just a million years, Gliese 710 will pass by at just over 1 ly.>>

http://asterisk.apod.com/vie ... 24#p117424

swainy wrote:Quote:
In particular, this data allowed astronomers to work out which stars we'd been closer to in the past and which we will meet in the future. It turns out that 156 stars fall into this category and that the Sun has a close encounter with another star (meaning an approach within 1 parsec) every 2 million years or so.

There is a big difference between a star passing within a couple of light years (which is what the statistics show happening every two million years), and passing near enough to the inner system to disrupt planetary orbits. The latter is obviously rare, since it doesn't appear to have happened in the last few billion years. And in the context of this discussion, it would make no difference if the object were a star or a black hole- either would have a similar effect. (Of course, the black hole would have a minimum mass of several suns, while a star might be a dwarf. Still, the two probably wouldn't be different in mass by more than an order of magnitude.)

swainy wrote:Quote:
In particular, this data allowed astronomers to work out which stars we'd been closer to in the past and which we will meet in the future. It turns out that 156 stars fall into this category and that the Sun has a close encounter with another star (meaning an approach within 1 parsec) every 2 million years or so.

That's not very often. According to Wikipedia, both of Proxima Centauri and Ross 248 are expected to come (just barely and briefly) inside our 1-parsec neighbourhood within the next 40.000 years.

Henning Makholm wrote:

swainy wrote:

http://www.technologyreview.com/blog/arxiv/24917/ wrote: In particular, this data allowed astronomers to work out which stars we'd been closer to in the past and which we will meet in the future. It turns out that 156 stars fall into this category and that the Sun has a close encounter with another star (meaning an approach within 1 parsec) every 2 million years or so.

That's not very often. According to Wikipedia, both of Proxima Centauri and Ross 248 are expected to come (just barely and briefly) inside our 1-parsec neighbourhood within the next 40.000 years.

Probably they meant to say "an approach within 1 light-year" where it would seriously perturb the Oort cloud.

http://en.wikipedia.org/wiki/Proxima_Centauri wrote:
<<Proxima Centauri is a red dwarf star approximately 4.2 light-years distant in the constellation of Centaurus. It was discovered in 1915 by Robert Innes, the Director of the Union Observatory in South Africa. Among the known stars, Proxima Centauri has been the closest star to the Sun for about 32,000 years and will be so for about another 33,000 years, after which the closest star to the Sun will be Ross 248. Proxima will make its closest approach to the Sun, coming within 3.11 light years of the latter, in approximately 26,700 years.>>

http://en.wikipedia.org/wiki/Ross_248 wrote:
<<Ross 248 (HH Andromedae) is a red dwarf star located approximately 10.3 light years from Earth in the constellation Andromeda. This star was first catalogued by Frank Elmore Ross in 1926 with his second list of proper motion stars. This star has about 12% of the Sun's mass and 16% of the Sun's radius, but only 0.2% of the Sun's luminosity. This is a flare star that occasionally increases in luminosity. With high probability there also appears to be a long-term variability with a period of 4.2 years. In 1950, this became the first star to have a small variation in magnitude attributed to spots on the photosphere.

The trajectory of Ross 248 will bring it closer to the Solar System in the future. In 1993 Matthews suggested that in about 33,000 years Ross 248 would be the closest star to the Sun, approaching within a minimum distance of 3.024 light-years (0.927 parsecs) in 36,000 years. However, it will recede thereafter and will again be further from the Sun than Proxima Centauri 42,000 years from now. The spacecraft Voyager 2 is traveling on a path headed roughly in the direction of Ross 248, and is expected to come within 1.76 light-years (0.54 parsecs) of the star in 40,176 years.>>