Science-astronomy 17 binary
Today Phil explains that YES, there are other planets out there and astonomers have a lot of methods for detecting them. Nearly have been found so far. We think there may be many billions of Earth-like planets in our galaxy. While Jupiter is nowhere near massive enough to initiate fusion in its core, there are even more massive objects out there that fall just short of that achievement as well called brown dwarfs.
Brown dwarfs, have a mass that places them between giant planets and small stars. Today we are talking about the life -- and death -- of stars. Low mass stars live a long time, fusing all their hydrogen into helium over a trillion years. More massive stars like the Sun live shorter lives. They fuse hydrogen into helium, and eventually helium into carbon and also some oxygen and neon. When this happens they expand, get brighter, and cool off, becoming red giants.
They lose most of their mass, exposing their cores, and then cool off over many billions of years. White dwarfs are incredibly hot and dense objects roughly the size of Earth. They also can form planetary nebulae: They only last a few millennia.
Massive stars fuse heavier elements in their cores than lower mass stars. This leads to the creation of heavier elements up to iron. Iron robs critical energy from the core, causing it to collapse.
The resulting supernova creates even more heavy elements, scattering them through space. Neutrons stars are incredibly dense, spin rapidly, and have very strong magnetic fields. Some of them we see as pulsars, flashing in brightness as they spin. Neutrons stars with the strongest magnetic fields are called magnetars, and are capable of colossal bursts of energy that can be detected over vast distances.
Stellar mass black holes form when a very massive star dies, and its core collapses. The core has to be more than about 2. Black holes come in different sizes, but for all of them, the escape velocity is greater than the speed of light, so nothing can escape, not matter or light. Last week we covered multiple star systems, but what if we added thousands or even millions of stars to the mix?
There are different kinds of clusters, though. Open clusters contain hundreds or thousands of stars held together by gravity. Globular clusters, on the other hand, are larger, have hundreds of thousands of stars, and are more spherical.
Astronomers study a lot of gorgeous things, but nebulae might be the most breathtakingly beautiful of them all. Nebulae are clouds of gas and dust in space. They can glow on their own or reflect light from nearby stars.
Stars are born in some nebulae, and create new ones as they die. Some nebulae are small and dense, others can be dozens or hundreds of light years across. The disk has grand spiral patterns in it, formed by the traffic jams of stars and nebulae, where stars are born. The central region is shaped like a bar, and is mostly old, red stars. The Milky Way is our neighborhood in the universe.
Galaxies contain gas, dust, and billions of stars or more. They come in four main shapes: Galaxies can collide, and grow in size by eating each other. Active galaxies pour out lots of energy, due to their central supermassive black holes gobbling down matter. Galaxies tend not to be loners, but instead exist in smaller groups and larger clusters. Clusters of galaxies also clump together to form superclusters, the largest structures in the Universe. In total, there are hundreds of billions of galaxies in the Universe.
Gamma-ray bursts are not only incredible to study, but their discovery has an epic story all its own. Today Phil takes you through some Cold War history and then dives into what we know. Bursts come in two rough varieties: Long ones are from hypernovae, massive stars exploding, sending out twin beams of matter and energy.
Short ones are from merging neutron stars. Both kinds are so energetic they are visible for billions of light years, and both are also the birth announcements of black holes. Today on Crash Course Astronomy, Phil dives into some very dark matters.
Galaxies and other large structures in the universe are created and shifted by a force we detect mostly indirectly, by observing its impact: Knowing that the universe is expanding and how quickly its expanding also allows us to run the clock backwards 14 billion years to the way the universe began - with a bang. The majority of the universe is made up of a currently mysterious entity that pervades space: We think this means the Universe will expand forever, even as our view of it shrinks while space expands faster all the time.
It started with a Big Bang, when the Universe was incredibly dense and hot. It expanded and cooled, going through multiple stages where different kinds of matter could form.
It underwent a phenomenally rapid expansion called inflation, which smoothed out much of the lumpiness in the matter. Normal matter formed atoms between 3 and 20 minutes after the bang, and the lumps left over from inflation formed the galaxies and larger structures we see today. But there is still hope that a new Universe will be born from it. Here it is, folks: In our final episode of Crash Course Astronomy, Phil gives the course a send off with a look at some of his favorite topics and the big questions that Astronomy allows us to ask.
Mars One plans one-way missions to Mars; the goal is not simply to explore, but to colonize the red planet. A one-way trip saves billions and eliminates the risk of a return voyage.
But can the crew survive in such utter isolation? Some candidates for the mission reflect on this challenge. Witness some of the most violent impacts in the universe, and meet the people protecting us from the fallout of these cosmic collisions.
More than three decades after the debut of Carl Sagan's ground-breaking and iconic series, "Cosmos: A Personal Voyage," it's time once again to set sail for the stars.
Host and astrophysicist Neil deGrasse Tyson sets off on the Ship of the Imagination to discover Earth's Cosmic Address and its coordinates in space and time. Viewers meet Renaissance Italy's Giordano Bruno, who had an epiphany about the infinite expanse of the universe. Then, Tyson walks across the Cosmic Calendar, on which all of time has been compressed into a year-at-a-glance calendar, from the Big Bang to the moment humans first make their appearance on the planet.
They evolve separately and have very little effect on each other. Close binaries are close to each other and are able to transfer mass from one another. They can also be classified based on how we observe them. Visual binaries are two stars separated enough that they can be viewed through a telescope or binoculars.
Eclipsing binaries are where the objects' orbits are at an angle that when one passes in front of the other it causes an eclipse , as seen from Earth.
Astrometric binaries are objects that seem to move around nothing as their companion object cannot be identified, it can only be inferred. The companion object may not be bright enough or may be hidden in the glare from the primary object.
A related classification though not a binary system is Optical binary which refers to objects that are so close together in the sky that they appear to be a binary system but are not. Such objects merely appear to be close together, but lie at different distances from the solar system. When binary minor planets are similar in size, they may be called " binary companions " instead of referring to the smaller body as a satellite.
Pluto and its largest moon Charon are sometimes described as a binary system because the barycenter center of mass of the two objects is not inside either of them. A binary star that has an orbital period of less than 30 years implies that the two system components are less than about 10 AU apart. Mass transfer occurs at some stage in most close binaries, profoundly affecting the evolution of the component stars.
If the two components are in a close binary and do not fill their Roche lobes , the system is considered a detached binary.
In a semidetached binary , one star fills its Roche lobe and mass transfer occurs. In a contact binary , both stars fill their Roche lobes. The evolution of close binaries depends on the initial masses of the two stars and their separation.
When the more-massive star evolves into a red giant first and fills its Roche lobe, material will spill through the inner Lagrangian point onto its companion, thereby affecting its companion's evolution. Mass transfer can also alter the separation and orbital period of the binary star.
In binaries that are initially widely separated, material escaping from the Roche lobe of the evolved red giant immerses the system in material, creating a common-envelope binary that contains the core of the red giant a white dwarf and the companion star. Friction causes the two components to approach, and thus the orbital period to shorten. The common envelope is ejected and a cataclysmic variable star is left, wherein the mass transfer from the companion to the white dwarf causes the periodic outbursts seen in novae , recurrent novae , dwarf novae , and symbiotic novae.
If one component of a close binary is massive enough, it may become a neutron star or black hole instead of a white dwarf.