What is the difference between a dwarf star and rogue planet?

NASA recently announced the discovery of a fairly cold Y dwarf star:


http://news.yahoo.com/blogs/technology-blog/nasa-spots-chilled-stars-cooler-human-body-004551421.html





For years, however, astronomers have also speculated that there may be rogue planets roaming around in space, unattached to a star. My question is, how do astronomers differentiate between a Y dwarf star and a roaming gas giant planet? Or are they the same thing?|||http://curious.astro.cornell.edu/question.php?number=548





It's apparently not a simple distinction.


I was curious also after reading the same NASA announcement.


Here's something I found from Cornell U.|||The distinction is based upon how the object formed, and how much mass it has.





Stars are formed by the conglomeration of independent gas clouds in interstellar space (not near a star) under the influence of gravity. Planets are formed when materials around a star condense around a rocky or icy core.





In order to have high enough temperatures in the core to burn hydrogen, an object needs to have a mass of at least 75 or so times that of Jupiter. Anything more massive than that is automatically considered a star.





This is a very insightful question, however, because as our observation abilities have improved, the lines between stars and planets become blurry. It is not always clear whether a body formed in stellar orbit or in interstellar space. Therefore, astronomers are currently using the following rule of thumb when an body is not orbiting a star:





The boundary between brown dwarfs and stars is still around 75 times the mass of Jupiter, as above, but the boundary between brown dwarfs and planets is set at around 13 times the mass of Jupiter, since that is the mass at which objects reach high enough central temperatures to burn deuterium (an isotope of hydrogen which undergoes nuclear burning at lower temperatures than regular hydrogen does).|||A star has nuclear fusion going on in its core. A planet, whether it is a rogue planet with no star, or whether it is planet orbiting star, does not have nuclear fusion going on in its core because of insufficient mass and pressure to initiate nuclear fusion at the center of the celestial body.





http://mbeck.hubpages.com/hub/the_differ鈥?/a>|||A dwarf star is massive compared to a less massive rogue planet though the latter might look voluminous. Such a star can be even more high in density and I don't need to go into how a dwarf star came about here.|||A Y dwarf star is a star that isn't very hot, and a rogue planet is a planet that isn't attached to a star, they both float alone in outer space.|||a dwarf star is small and a rogue planet is big.


i called some guys a nasa and thats what they told me to tell you.


hope this helps :)|||it's chemical composition|||According to current astronomical theory, planets and stars are created by essentially the same process: matter accretion. They are pulled together by gravity, and they accrete (that is, pull in and incorporate) the matter around them. The essential difference is one of mass: the star has more mass, the planet less.





As a mass accretes, it gets hotter. This is because infalling matter gives up potential energy when it falls toward a gravity well; another way of looking at it is that there is more friction for an object coming into a more crowded area, and friction means heat. All accreted objects heat up. A star is one that heats up so much that the predominant gas present in the universe, hydrogen, fuses into helium. This "ignition" of nuclear fusion, allowing the star to produce more energy than it absorbs, is it's hallmark. If accretion stops before that happens, the body is a planet. Large ones are termed "brown" because they are radiating heat produced by accretion, but have no internal fusion heat production capability of their own. In this sense even the Earth is a brown planet, as it still radiates its accretion heat.





Heat from internal radioactivity (fission) is regarded as no different from accretion heat. There's just not enough fissiles in the galactic dust to build a fission star.





A dwarf star is just a small star. It might even be extremely hot, such as white dwarfs (the remnants of stars like the sun at the end of their lives) or a neutron star, which is dwarf in the extreme. Likewise, a rogue planet is any planet that is not orbiting a star, not necessarily one that has grown large enough to approach stardom.