How close could a brown or red dwarf get without being seen?

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willpittenger

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I read a SciFi book (<i>Nemisis</i>) where a red or brown dwarf (I do not remember which) was hiding behind a cloud really close. (No more than 2 light years.) In the book, it was moving through the cloud and would move through or close to our solar system. In the book, it was expected to change planetary orbits.<br /><br />I am not worried about that scenario as much as could one be orbiting the Sun. Such a star could hurl Oort cloud objects into the solar system. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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qso1

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If one takes Alpha Centauri as an example, a red dwarf called Proxima Centauri is thought but not known for sure to be in orbit around AC at about 13,000 Au distance. 1 Ly is 62,000 + Au). Well within 1 Ly of AC.<br /><br />The book you read mentions Nemesis which is a theoretical star of just this type (Red, or possibly brown dwarf) in orbit around the Sun. So far actual astronomical observations do not support such a star but it has not been ruled out. If a star is in orbit well within a light year of the Sun. If its a red dwarf, it would probably be visible through a moderately powerful backyard telescope, maybe a Celestron 8. And it would only be visible if not behind a dust cloud. If it does exist, it probably has disturbed the Oort cloud in times past. The Nemesis scenario was theorized to have caused such disturbances which led theoretically to mass extinctions every 32 million years.<br /><br />Heres a couple links:<br />http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961130b1.html<br /><br />http://swanson.bol.ucla.edu/ <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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willpittenger

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So how much different would the brown dwarf be?<br /><br />Also, Nemesis would need to perturb the Oort cloud more often than every 32 million years. I say that as some objects would miss Earth. <br /><br />Since you and the posts mentioned 32 million years, how big of an orbit would that be? Wikipedia has 50,000 to 100,000 AU. How reliable is such a large range?<br /><br />From the Wikipedia page for the Nemesis novel: "The red dwarf star in the book turns out not to be this companion; it is simply passing through the solar system." <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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qso1

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A brown dwarf would be less of a star than a red dwarf. It can be thought of as something just barely ignited.<br /><br />The best explanation I can find is here:<br />http://www.solstation.com/stars/pc10bd.htm <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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qso1

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This one is red dwarfs.<br /><br />http://www.solstation.com/stars/pc10rds.htm <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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qso1

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A dwarf star passing through the solar system would probably be more of a threat to us by way of the Oort cloud disturbances you mentioned earlier. If we detected such a star however, it would be decades or perhaps millinia before something from the Oort cloud would finally get within close range of Earth. This would depend on the approach speed of the star in question and the time it takes for gravitationally disturbed objects to reach Earth. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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newtonian

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willpittenger - I will research before responding better - but scientist John Matese independently examined perturbations of Oort cloud orbits and submitted a model explaining the observations.<br /><br />This model posits that a very large planet, larger than Jupiter but smaller than a brown dwarf, is perturbing orbits in the Oort cloud.<br /><br />Alas, the link was lost with the last SDC crash.<br /><br />Hopefully someone can find it.<br /><br />He was at LSU (Louisiana State University).
 
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newtonian

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willpittenger - See Scientific American, April, 2000 at:<br /><br />www.sciam.com<br /><br />www.sciamdigital.com<br /><br />Also January, 2006 Scientific American<br /><br />From the 2/00 issue an excerpt:<br /><br />“Scientific American,” April, 2000, page 77 ff (= plus following pages)<br /><br /><br />“THE DISCOVERY OF BROWN DWARFS, by Gibor Basri<br />Less massive than stars but more massive than planets, brown dwarfs were long assumed to be rare. New sky surveys, however, show that the objects may be as common as stars”<br /><br />The article goes on to show that brown dwarfs were only recently confirmed to exist by actual observation , discovered in 1995 (I.e. indisputable evidence presented).<br /><br />On page 77 Sciam shows two photos of a brown dwarf, classified Gliese 229B, alongside its companion red dwarf star, classified Gl 229A. The brown dwarf is further from the much larger red dwarf than Pluto is from our sun, namely: c. 6 billion kilometers away from Gl 229A.<br /><br />On p. 78 Sciam images other brown dwarfs plus Gl229B. Brown dwarf PPL 15 was located in a search of young star clusters since brown dwarfs are brighter when young. It was found in the 120 million year old Pleiades Cluster.<br /><br />Obviously old brown dwarfs would be harder to observe as they become less luminous. <br /><br />Another way to locate brown dwarfs would be to use telescope instruments sensitive to faint red sources of light (but you must distinguish between close brown dwarfs and distant red giants).<br /><br />This simply picks a field of observation, and thus the brown dwarfs discovered by this method are called “field” brown dwarfs. The first brown dwarf discovered by this method was in 1997 and is classified Kelu-1. It is also imaged (shown) on page 78.<br /><br />Brown dwarfs could make up a significant portion of dark matter, currently invisible to us.<br /><br />Interestingly the
 
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mikeemmert

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Here's a thread that appeared in SS&A a while back that has quite a bit on the Nemesis/close stellar encounter scenario, including a lot of links that were dug up of relevance to the question.<br /><br />As far as how far away a brown dwarf can be seen, by best guess is about 600 AU. That would be at the same brightness as 2003 UB313. Since all brown dwarfs are about the same diameter as Jupiter, that makes it easier to come up with an estimate. They are about 40 times the diameter of 2003 UB313, giving them 1600 times the area, and the fourth root of 1600 is ~6. Xena is ~100 AU away right now.
 
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nexium

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600 AU is a reasonable limit, if the same size and surface temprtature as Jupiter. Jupiter is about 3 AU from the Sun, so this is 200 times farther and thus 40,000 times dimmer in infrared, and that assumes Jupiter reflects no infrared from the Sun. Likely not so. A million times dimmer in infrared (than Jupiter) and essentually no visable light, means we can detect it only when it ocults a distant star. Are there any extensive programs for detecting the occut of very dim stars = 24 magnetude? Would the ocult be likely to last more than one minute? Can we detect partial occult with CCD = charge coupled device at the maximumum usable magnification of a world class telescope? Neil
 
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doubletruncation

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<i>Are there any extensive programs for detecting the occut of very dim stars = 24 magnetude?</i> <br /><br />There are in fact some deep occultation surveys (I believe predominately for comets). See for example: http://www.tanet2.net.tw/english/news_&_events/news_briefs/volume_12/TAOS.html<br /><br /><i>Would the ocult be likely to last more than one minute?</i><br /><br />Depends on the size of the occulting body, the distance to it, and the chord of the occultation. But, for example, from the recent paper yielding a direct measurement of the size of 2003 UB313 (http://xxx.lanl.gov/abs/astro-ph/0604245) Brown et al mention that the KBO moved ~30 mas over the course of the ~120 second exposures, and they measure a size of ~30 mas for the KBO. So an occultation by 2003 UB313 would last ~2 minutes at most (less for a chord that doesn't cut across the diameter).<br /><br /><i>Can we detect partial occult with CCD = charge coupled device at the maximumum usable magnification of a world class telescope?</i><br /><br />You wouldn't hope to resolve the surface of the occulting body, so magnification doesn't really apply (Note that 2003 UB313 is just barely resolved by Hubble). Instead you'd monitor a bunch of stars and just watch to see if any of them disappears for a minute or two. I think you'd really need a fast read-out CCD, a wide-field of view, and a large telescope (though of course getting the last two simultaneously is always a challenge). <div class="Discussion_UserSignature"> </div>
 
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tony873004

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Xena has a very high aldebo. A brown dwarf would have a lower aldebo than Xena, so it would need to be even closer.<br /><br />But brightness isn't the only important thing in making something easy to discover. Keep in mind that Xena is the 4th brightest KBO. Why were over 500 dimmer ones discovered before it? It's because Xena, at its distance, has a very slow proper motion. Earlier surveys missed it because its speed was below a certain threshold. Only when Sedna inspired Mike Brown et al to lower the threshold, was Xena discovered.<br /><br />Something at 600 AU will be even slower, and hence difficult to distinguish from a background star.<br /><br />Regarding Nemesis stirring up the Oort Cloud on a periodic basis and sending comets crashing into Earth, here's something I don't understand:<br /><br />Oort Cloud comets are believed to be at about 60,000 AU. They should have an orbital speed of ~120 m/s. For them to drop to the inner solar system, they would need to have this orbital speed reduced to less than ~1.5 m/s. Comets whose velocity is changed to ~2m/s won't drop much closer to the Sun than Jupiter. ~5 m/s and above, and they don't even make it as close to the Sun as the Kuiper Belt. So the inner solar system is a very small target.<br /><br />And those that do get sent to the inner solar system have another lottery they must win. Earth is a very small target in the inner solar system. To get hit, the comet must be in the ecliptic when it crosses the 1AU mark. And even if it is, The Earth, with its 12000 km diameter and 1 billion km orbital track around the Sun, only occupies 1/75000 of its orbit at a time.<br /><br />So it would take millions of comets falling to the inner solar system for every hit. Would Nemesis be able to alter the velocities of millions of comets such that their new orbital velocities are in the small window of 0-1.5 m/s?
 
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willpittenger

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It also took the latest Hubble instruments to resolve Pluto and Charon as more than points of light. Previously, even Hubble only saw points. They were settling for using Pluto and Charon going in front of each other to map them. That was probably slow going and lower res than direct observation. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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nexium

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Red dwarf typically means a class m star. Hubble can detect them thousands of light years away, and has no trouble detecting Centarii Proxima, nor Barnard's Star. Brown dwarf stars have less mass, but more mass than Jupiter. Brown dwarf's typically produce negligible visable light, but they do radiate a small amount of infra red light, and are thus detectable with an infrared telescope more than a light year away, even if they have a color temperature of 73 degrees k = -200 degrees c. Brown dwarfs have been detected up to 500 light years (I think) when they orbit main sequence stars, as they behave much like very massive exoplanets.
 
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willpittenger

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<blockquote><font class="small">In reply to:</font><hr /><p>Brown dwarfs have been detected up to 500 light years (I think) when they orbit main sequence stars, as they behave much like very massive exoplanets.<p><hr /></p></p></blockquote><br />Forget the "main sequence star" part. We were talking about a brown (or red) dwarf on its own rather than part of a system. Any system would have planets or other dwarfs orbiting the dwarf in question. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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alokmohan

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Can we call brown dwarf plane mos?Any way it the dark matter we are looking since 80s.
 
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qso1

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Brown dwarfs are distinct enough and lean more towards being stars than planets. That is if one considers a star to be something that sustains fusion processes however small. They would not probably be considered planemos. And I doubt brown dwarfs have enough collective mass to be the dark matter cosmologists are looking for. There is an incredibly vast amount of space between any star system which makes brown dwarfs unlikley candidates for missing mass. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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willpittenger

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I do remember that was once considered one possibility. Later theories though revolve around weird particles and states of matters if I understand Brian Greene's book Elegant Universe correctly. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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qso1

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I recall that as well but when I try to imagine how many brown dwarfs it would take to account for dark matter...my thoughts lead me to conclude we should already see hundreds of them within 1 Ly of Earth in order to account for the missing mass refered to as dark matter.<br /><br />And to answer your original question, I'm going to estimate that a brown dwarf could get as close as 1-2Ly without being detected. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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doubletruncation

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Microlensing surveys over the last decade and a half or so have put strong constraints on how much of the dark matter could be accounted for by MACHOS (free-floating planets, asteroids, brown dwarfs etc). Interestingly these surveys have found positive detections which suggest that 20% of the mass of the halo may be due to MACHOS like these. However it's also clear that there isn't enough of it to account for even most of the dark matter.<br /><br />Just from a google search, there is a pretty interesting website discussing this at:<br />http://web.mit.edu/~redingtn/www/netadv/specr/78/node1.html <div class="Discussion_UserSignature"> </div>
 
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nexium

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Brown dwarfs average 1% of the average mass of ordinary stars. Planets and asteroids average 0.001 % If the the 20% is correct and the calculated mass of halos is correct, these halo bodies out number the visable stars, by perhaps 1000 times, excluding small asteroids. Likely free floating bodies are also common inside galaxies. In addition to the free floating bodies you specified, there are likely many large comets, white dwarfs, neutron stars, black holes, and quark stars, both inside galaxies and in halos. We may not have charted a billionth part of what is within 13.7 light years, or so. Estimates may be off by a lot. Neil
 
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qso1

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Thanks doubletruncation and nexium. I kind of recall there not being enough objects to account for the missing matter mass as pointed out by doubletruncation while at the same time, as nexium points out, we don't really yet know for sure how many objects are still undetected. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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alokmohan

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Dark matter is still open question.We dont know how much dark matter is there in the Galaxy,Leave aside Universe.But dark mtter is real thing.
 
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alokmohan

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The motion of the stars and galaxies are influenced by material which has not yet been detected. Much of this invisible dark matter, which astronomers call "missing mass", could be made up of brown dwarfs - objects whose mass is between twice that of Jupiter and the lower mass limit for nuclear reactions (0.08 times the mass of our sun). Brown dwarfs are basically failed stars which did not have enough density at their cores to start nuclear fusion. The conversion of hydrogen into helium in a star's core by nuclear fusion is what fuels a star. This fusion process requires an extremely high density at the star's core to compress the hydrogen atoms together and produce helium. Another component of the missing mass may be the burned-out cores of dead stars. When most stars run out of fuel and their fusion reactions stop, they eventually cool off to the point where they no longer radiate enough visible light to be detected by optical telescopes. <br />Brown dwarfs are very dim and cool compared with stars. The best hope for finding brown dwarfs is in using infrared telescopes, which can detect the heat from these objects even though they are too cool to radiate visible light. Many brown dwarfs have also been discovered embedded in large clouds of gas and dust. Since infrared radiation can penetrate through the dusty regions of space, brown dwarfs can be discovered by infrared telescopes, even deep within thick clouds. Recently, 2MASS (Two Micron All Sky Survey) data revealed the coolest known brown dwarf. To the right is an infrared image of the Trapezium star cluster in the Orion Nebula. This image was part of a survey done at the United Kingdom Infrared Telescope (UKIRT) in which over 100 brown dwarf candidates were identified in the infrared. <br /><br /><br /> <br />Philip Lucas (Univ. Hertfordshire) and Patrick Roche (Univ. Oxford), UKIRT <br /> <br />Artist's rendition (Robert Hurt, IPAC) The discovery of the objects which make up the missing mass will also give astr
 
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