On the other side of the range of stars lie the supermassive, superluminous, and very unstable stars.  It is believed that all of them are supernova progenitors. While extremely rare, gravitational collapse of star forming clouds can result in the formation of stars with 20-200 solar masses.  They live violent and short lives of only a few million years.  They burn through their available hydrogen very quickly, with surface temperatures on the order of 30,000 to 200,000K, or about 6 to 35 times that of the sun.  Especially towards the end of their short lives, they experience a ‘wind’, which ejects over a billion times the mass of our sun’s wind.  This extreme mass loss results in emission lines, and this is how we can detect WR stars.
The most luminous stars discovered reside within the Tarantula nebula in the LMC.  While still very bright in the visual spectrum, they produce most of their luminosity in the UV and soft X-rays due to their high surface temperature.  Their stellar winds sculpt the surrounding gas and dust, and will likely clear out the star forming material within the nebula in the near future.
The Wolf-Rayet characteristics are thought to exist for all supermassive stars during the later stages of their lives. As a star this massive dies, it will eject all of it’s outer envelope of hydrogen, leaving a massive, superluminous blue core rich in metals.  This core is destined to undergo a core collapse supernova.  There is nothing that can support a core of this mass against complete collapse, and it will become a singularity of infinite density, or a black hole.

1. Shara, M. M.; Faherty, J. K.; Zurek, D.; Moffat, A. F. J.; Gerke, J.; Doyon, R.; Artigau, E.; Drissen, L. (2012). “A Near-Infrared Survey of the Inner Galactic Plane for Wolf-Rayet Stars. Ii. Going Fainter: 71 More New W-R Stars”. The Astronomical Journal 143 (6): 149. arXiv:1106.2196. Bibcode:2012AJ….143..149S. doi:10.1088/0004-6256/143/6/149. edit
2. Sander, A.; Hamann, W. -R.; Todt, H. (2012). “The Galactic WC stars”. Astronomy & Astrophysics 540: A144. arXiv:1201.6354. Bibcode:2012A&A…540A.144S. doi:10.1051/0004-6361/201117830. edit

Scientists at the RHIC (Relativistic Heavy Ion Collider) in Long Island are preforming similar experiments to the LHC, trying the probe the one of most fundamental, unconfined form of matter, the quark gluon plasma. This type of plasma one can think of as the ‘melted’ form of nuclear matter, because it is essentially a plasma so hot and dense that all of the protons and neutrons (collectively known as Hadrons because they are each made up of 3 quarks) within the gas have melted into the constitute particles known as quarks, as well as the force carrying particles of the strong nuclear force, gluons, that originally bound these quarks together in their proton and neutron forms. It takes very high energies to recreate these conditions in the collider, but ironically enough, when scientists tried to find the ‘melting’ point of nuclear matter after underestimating the energy needed the first time, their second attempt they overestimated and created the QGP without being able observe the physics of the transition. Scientists at RHIC are essentially trying recreate the phase diagram of nuclear matter, just like water has a phase diagram, telling us whether it is a liquid, ice, or vapor at a given temperature and density. They have recently come close to finding what they think might be a critical point of the phase diagram. Signatures of latent heat, and erratic behavior the nuclear fluid suggest so. latent heat can be thought as heat being taken in by the matter and used to change it phase rather than heat it more. It is the same effect that makes water stay at its boiling point temperature until all the water is vapor; Heat must be put in to make the complete transition, before the temperature of the fluid is to be raise more.

Advanced particle research such as this is also crucial for astrophysics and astronomy advancement, because as astronomers probed farther distances, and farther back in time, they have discovered that the universe is expanding. But not only that, it has been expanding from a singularity, a point. When astronomers look back to the beginnings of the universe, they are actually seeing the light from the early universe, and the image shows that the universe was just a hot dense ball of energetic matter. Before 380,000 years after the big bang, it was too hot and dense for light to even exist unconfined for us to see now, but we are still able to probe back indirectly. When the universe was small, and all the energy and matter of it was packed in this tiny space, the conditions were so extremely hot and dense, that scientists know now the QGP must have been the entire form of the universe. Understanding how this phase of matter behaves is crucial for understanding how the early universe created the initial conditions that lead to the universe as we see it now. For the most part, we have a very clear story of how everything in the universe formed from a few microseconds after the big bang, but we don’t know what happened before those couple of microseconds to create the conditions of what we see microseconds after the big bang.

Sources/Further Reading:

http://www.sciencedaily.com/releases/2014/04/140404135856.htm http://en.wikipedia.org/wiki/Quark%E2%80%93gluon_plasma

From the time we were first taught about outer space in elementary school, we learned that interstellar space was a vacuum. Basically, we could assume that all mass in the universe was concentrated at stars, planets, or other massive objects while the space between them was a perfectly empty void. While this is a good approximation, it is not entirely accurate.

Our text has made it clear that interstellar space is full of particles and energy, from photons to neutrinos to the interstellar medium to cosmic background radiation. If it did not have any of these things, space would be a perfect vacuum with no energy, stuck at absolute zero (0K). However, this is not the case. Even in the regions of space furthest from any heat sources, the cosmic background radiation keeps interstellar space at a temperature of about 3K. This only increases as we move toward stars, meaning there must be massive particles in space.

But how many? The most widely accepted figure for the density of interstellar space (M. Tadokoro, 1968) is calculated to be 7 x 10^-29 grams per cubic centimeter, which translates to about 40 hydrogen atoms per cubic meter. The best vacuum ever constructed on Earth was done at CERN at reported to achieve a density of about 1000 atoms per cubic centimeter. While this is astonishingly low, it is still over 2 million times more dense than interstellar space! No, space is not a perfect vacuum, but it is certainly the best approximation that exists.

Sources and Further Reading:

http://en.wikipedia.org/wiki/Vacuum#Outer_space

http://adsabs.harvard.edu/abs/1968PASJ…20..230T

http://www.ccmr.cornell.edu/education/ask/?quid=1026

Our reading today mentioned the ultimate fate of nearly all main sequence stars. At the end of the white dwarf stage, the star cools and begins to crystallize. The star, made almost entirely of carbon and oxygen, crystallizes first at the core and eventually becomes a “cold, dark, Earth-size sphere of crystallized carbon and oxygen floating through the depths of space” (Carroll and Ostlie, p. 576). However, the text was unclear about the abundance of these floating diamonds. My understanding was that it takes so long for the cooling process to occur that none of these objects exist yet. This is not necessarily the case.

First of all, a fully crystallized star would emit little to no radiation whatsoever. As such, they would be nearly impossible to detect with modern technology. The only technique that seems plausible for detection is if a crystallized star was part of a binary system so it would cause some wobble in a brighter star. Even in that case, a crystallized star would be indistinguishable from an exoplanet.

Image Source: Harvard-Smithsonian Center for Astrophysics

Fortunately, between 1995 and 2004 a star was detected 50 light-years from Earth that pulsated and had a low luminosity, both signals of a crystallizing star. It was finally determined that between 80 and 90 percent of the star’s mass has crystallized, meaning it still emits just enough radiation to be detected. The final 10 percent will still take many millions of years to completely crystallize, but as is the star has been nicknamed “Lucy” after its diamond-like qualities. Estimations set the diamond in the core of the star at an amazing 10 billion trillion trillion carats! As our technology improves, it is likely that we will detect even more of these massive diamonds.

Sources and Further Reading:

http://en.wikipedia.org/wiki/BPM_37093

http://www.spacetoday.org/DeepSpace/Stars/WhiteDwarfs/LucyDiamondStarWhiteDwarf.html

http://starryskies.com/articles/2004/02/diamond.html

In January 2014, the European Southern Observatory’s VLT recently gave us some fantastic images of a very small star of low luminosity, WISE J104915.57-531906.1B, now known as Luhman 16B.  It is a brown dwarf, a class of small stars with very cool surface temperatures. Luhman 16B and its binary partner are the closest brown dwarfs yet discovered at around 6 light years from earth. They blur the boundary between Jupiter-like substellar objects and stars, sustaining only minimal fusion in their cores and exhibiting surface weather that is similar to our gas giant planets.  Above about 13 Jupiter Masses, deuterium fusion can occur.  Above about 65 Jupiter Masses, fusion of lithium can occur as well.  To be technically considered a star, an object should be fusing hydrogen, and this occurs above 75-80 Jupiter masses.  In any case, these stars are very difficult to detect in the visual wavelengths, since they emit most of their energy in the infrared.

Like other dwarf stars of low luminosity, they can become incredibly dense.  Since there is very little pressure from fusion to sustain an expanded gas envelope, the object is supported by the thermal energy left over from initial gravitational collapse.  As the star ages, it consistently shrinks, supported at first by coulomb pressure and later by electron degeneracy pressure.  Of particular interest is their usual radii.  For a brown-dwarf star that has had time to settle, it can contain perhaps 20 times the mass of Jupiter in as little as 1.5 Jupiter Radii.

Many brown dwarfs exhibit extreme weather.  They tend to rotate rapidly and sustain convection throughout, which in turn creates strong and variable magnetic fields.  Brown Dwarfs have been identified as X-ray sources, likely the result of flares due to magnetic activity.

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1. Tables VII, VIII, Empirical bolometric corrections for the main-sequence, G. M. H. J. Habets and J. R. W. Heinze, Astronomy and Astrophysics Supplement Series 46 (November 1981), pp. 193–237, Bibcode: 1981A&AS…46..193H. Luminosities are derived from M_bol figures, using M_bol(☉)=4.75.
2. T. J. Dupuy & A. L. Kraus; Kraus (2013). “Distances, Luminosities, and Temperatures of the Coldest Known Substellar Objects”. Science. published online 5 September 2013 (6153): 1492–1495. arXiv:1309.1422. Bibcode:2013arXiv1309.1422D. doi:10.1126/science.1241917.
3. First weather map of a brown Dwarf”           http://www.eso.org/public/news/eso1404/  “
4. “X-rays from a Brown Dwarf’s Corona”. April 14, 2003.

image from wikipedia

Many supermassive black holes, hundreds of thousands to billion times the massive of our sun, have been found at the center of not only our galaxy, but in many others. It seems that this supermassive black hole is a characterizing feature of most galaxies, responsible for holding the group of stars the galaxy together. Although theories of dark matter are still needed to fully describe the gravitational stability of galaxies, this supermassive black hole is responsible for the large density of stars at the center of our galaxy and others.

There are two curious properties of black holes that makes the supermassive black holes unlike typically stellar-size black holes, which are on the order of one solar mass up to 33 solar masses. Any black hole’s size is determined by its Schwarzschild radius, the radius in the gravitational field in which if an object passed it not even light can escape it, and this radius is directly proportional to mass. Because of this property, density and tidal forces can be expressed directly in terms of mass and not mass and radius. The density is equal to the mass divided by the volume of the black hole, which is proportional to the radius cubed, thus the density is proportional to m^-2. Tidal forces, the difference in the strength gravity between successive radii, can be also expressed as proportional to m^-2. What this means for supermassive black holes is that they are not very dense and have very weak tidal forces. If you could stand right above the event horizon of a 10 million solar mass black hole, you would feel similar tidal forces we have on Earth. This means stars can exist close to the black holes without getting ripped apart.

Formation of these gigantic black holes is still a process being researched. Black holes are only made from massive stars collapsing in a supernova explosion that leaves behind a black hole. Because there is an upper limit on the size of these massive stars, there is also an upper limit on the size of the black hole left. Scientists can then predict based off how much gas and matter is left near the black hole, how big it will grow to be based off how much of this matter is accreted inside the black hole. But based on these size calculations alone, we would never expect to find supermassive black holes, unless black holes themselves collided together to form even bigger black holes. It is believed now that supermassive black holes are made from older black holes that over time have collided to form bigger and bigger black holes, which then our galaxy forms around. When two older dwarf galaxies collide, it is very often the case that none of the stars collide or touch, but since black holes are at the center and have a much bigger pull of gravity, it is often the case that they combine. But, when scientists have looked further stellar distances back in time to see primordial dwarf galaxies, they have found that these smaller, ancient galaxies have intermediate size black holes on the order of 1,000 to 10,000 solar masses, which was bigger than expected from theoretical calculations based on accretion rates.  The fact that the black holes are bigger than predicted suggests that black holes are somehow getting bigger faster than just based on the gas accreted into them. But from what we know about these dwarf galaxies, they originated from a very isolated existence, and we wouldn’t expect them to be moving near each other often enough to collide and form these bigger black holes. We know that these galaxies begin to move and collide in the future enough to form the supermassive black holes we see today, but it is unclear how these primordial black holes initially formed.

Sources:

http://www.sciencedaily.com/releases/2014/03/140326170320.htm

http://en.wikipedia.org/wiki/Supermassive_black_hole

Our textbook reading for today made supernovae sound like some of the most exciting natural phenomena humans have ever observed. A star shining so brightly that it is visible during the daytime is almost unfathomable. I immediately began trying to figure out if a supernova would be visible from Earth during my lifetime. Supernovae are detected often in other galaxies, and a supernova in a neighboring galaxy such as Andromeda would definitely be visible to the naked eye. But for maximum effect, I am most curious about a supernova in our galaxy.

According to the textbook, the last supernova to occur in the Milky Way galaxy was of η Carinae beginning in 1837 and fluctuating in brightness for twenty years. Also, the textbook states that supernovae occur (on average) once every hundred years in any one galaxy. With the last supernova occurring 177 years ago, it sounds like we are long overdue!!

Image Source: annesastronomynews.com/photo-gallery-ii/

Researchers agree with that sentiment. According to a probabilistic model constructed at The Ohio State University, there is nearly a 100% chance that a supernova will occur in the Milky Way within the next 50 years. Unfortunately, they concluded that there is only a 10-50% chance (dependent on the observer’s location on the Earth’s surface and the position of the supernova in the sky) that it will be visible from Earth. A visible supernova in my lifetime is not the foregone conclusion that one might expect, but is certainly still an exciting possibility.

Sources and Further Reading:

http://researchnews.osu.edu/archive/supernova50.htm

http://scienceblogs.com/startswithabang/2012/01/26/our-galaxys-next-supernova/

Beyond the orbit of Neptune and the Keiper belt,  lies a vast region of our solar system known as the Oort Cloud filled with icy bodies weakly bound to the sun in very long orbits. The Oort cloud is defined as a region of space that is spherical shell around the sun starting at 2,000 AU away from the sun, the beginning of the inner Oort cloud, and ending at about 50,000 AU away, the outer Oort cloud. The absolute maximum distance the Oort cloud extends to is usually defined by the Sun’s tidal truncation radius, which is 100,000 to 200,000 AU.  This is the radius away from the sun at which the gravitational pull of the sun is about equal to the galactic ‘tide,’ which is essentially the gravitational pull of other stars and the galaxy as a whole.

image from wikipedia

The farther out in the Oort cloud an object is, the weaker the pull of sun is, and thus the pull of gravity by the galactic tide plays a much larger role in changing the motion of the object. Galactic tide is similar to ocean tides in that as we orbit the galaxy, gravity pulls more strongly on one side of the solar system than the other, causing the sun’s field of gravity to warp from a spherical shape to more of an ellipsoid periodically. The inner planets like Earth never notice this effect because we are so close to the sun, the galactic tide would never shake us from the strong pull of the sun, but objects very far out in the Oort cloud are.

The cloud was named after Jan Oort, who proposed that comets originated from this cloud of icy bodies due to a slight displacement from its orbit that pulled it into a long elliptical orbit close to the sun. At the time, it was speculative to what would cause the displacement creating the comet’s orbit, but with computer simulations, many think that as much as 90% of comet’s orbits are made from changes in the periodic galactic tide versus random events such as stars or giant molecular clouds just happening to get closer to the solar system.

It was first proposed by Newton and showed by Edmond Halley (of which the famous comet is named after) that comets must orbit the sun in long elliptical orbits lasting hundreds to thousands of years. The only reason we can see comets is because as they approach the perihelion or their orbit, at 3-4 AU, the flux (energy/area) of the sun’s energy hitting the comet increases enough to melt the ice on the comet, creating a gas cloud on the surface called a coma. A dust tail is then formed due to radiation pressure from the sun and solar winds pushing dust off the cloud. This tail of matter coming off the comet is then illuminated by the sun’s UV light exciting the gas causing emission of visible wavelengths. Thus, making comet’s very noticable in the night sky for this time. Once the comet passes the perihelion, it then begins to freeze again, going dark in the night sky. This effect is what enabled Halley and others to learn about these far objects without large, advanced telescopes.

image from wikipedia

As scientists improve telescopes, especially in the infrared range, we are finding more and more Oort objects. Since all these objects are invisible to us the visible range, infrared telescopes are useful for detecting the larger objects that could have core heat signature in the infared range.  Sedna and VP 2113 are two inner Oort cloud objects that have been discovered in the past 10 years. We also now believe that much of the outer Oort cloud formed with the rest of the solar system, while the very outer edges may act like an ‘eddy’ in the tides of galaxy collecting objects that exist in the interstellar medium between stars. What remains a challenge however is detecting the objects in the outer Oort cloud, as it takes precision equipment as well as luck. There remain many questions on the distribution and size of these objects, as well as how they formed, and their evolution over time.

Sources used:

http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong

http://www.nasa.gov/content/nasa-supported-research-helps-redefine-solar-systems-edge/#.Uzwnlq1dWr8

http://en.wikipedia.org/wiki/Oort_cloud

http://en.wikipedia.org/wiki/Comet

http://www.space.com/53-comets-formation-discovery-and-exploration.html

One of the most well known Bible passages is God’s promise to Abraham, which reads: “ I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore.” -Genesis 22:17 (NIV). While sitting on the beach over spring break, I wondered which of those two quantities was larger.

According to modern astronomers, it is possible to estimate the number of stars in the universe to within at least a few orders of magnitude. By taking the number of stars in our galaxy (somewhere between 10^11 and 10^12) and multiplying by the number of galaxies (another 10^12), it can be estimated that there are somewhere on the order of 10^24 stars in the observable universe. Obviously, this is a very rough estimate, but this is the best estimate available and definitely seems reasonable.

Surprisingly, we know far less about the number of grains of sand on our own planet. Researchers in Hawaii supposedly took the number of grains in a teaspoon of sand and used satellite imagery of the Earth’s surface to estimate the volume of sand on the face on the Earth. They came up with about 10^19 grains of sand. I could not find their methodology posted anywhere, but this seems like a very low estimate for a number of reasons. For one, there is no way to estimate the depth of sand from satellite imagery. Giant dunes in the Sahara obviously contain more sand than a comparable surface area in a sandbox. Furthermore, they say that they only used beaches and deserts in their estimation. I would propose that there are MANY more areas for sand to exist (the floor of the ocean being the greatest omission).

Of course, God’s promise to Abraham specified only sand on the seashore. Either way, I think there is still some work to be done before answering this age-old question.

Sources and Further Reading:

http://www.npr.org/blogs/krulwich/2012/09/17/161096233/which-is-greater-the-number-of-sand-grains-on-earth-or-stars-in-the-sky

http://www.esa.int/Our_Activities/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe

When I searched for astrophysics news, I was pleasantly surprised to find one about galaxy interaction. Galaxy interaction as a topic is rarely discussed enough, even when it occurs on a daily basis and will likely happen to our own galaxy, given enough time. Recently, the picture above clearly highlighted two galaxies that are nearing collision and their vastly different histories. These two galaxies, NGC 1316 and NGC 1317 , although neighbors, have done dramatically differing amounts in getting to where they are.

NGC 1316, as seen in the picture, has pretty clear residue and aftermath of more outer layers of its galaxy that are not condensed and highly orbiting, rather, just residually following. To follow the article, this is indicative of galaxy collision, or “galaxy serial killer,” as a result of the clear larger amount of stars and the dust lanes that fill the space between the clusters of stars. The imagery used by the article is that this galaxy “swallowed” this other galaxy to create its current form.

What interested me about this topic to begin with is a fairly popular gif image created that illustrates the impending collision between the Milky Way and the Andromeda galaxies, believed to look like the image below.

While is image is stunningly beautiful and appears to create a new sort of star or black hole, the idea that stars will collide is unlikely at best due to the raw space between stars in both galaxies. Using the Hubble Space Telescope data, researchers found that this collision of galaxies is inevitable for the foreseeable future, and that the collision of black holes would lead to a new one due to the nature of supermassive black holes, but this process itself, on top of the billion years we have before the collision, could take millions longer. The collision is again enjoyable to think about as a thought, due to its implications and the future thought required to imagine if there would even be life on earth to observe what would happen during that time.

Sources:

Carroll, Ostlie. An Introduction to Modern Astrophysics.

http://www.sciencedaily.com/releases/2014/04/140402095846.htm