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Astrophysics
Astrophysics is the scientific discipline concerned with the events that are taking place on the grandest of stages; the universe. Questions about the formation and evolution of the planets, solar systems, stars, and galaxies found within the universe, as well as questions regarding black holes, cosmic rays, particle and nuclear astrophysics, nucleosynthesis, and magnetohydrodynamics should be directed here.
1,304 Questions
Why mass and energy curve the space and time?
Mass and energy curve space and time according to Einstein's theory of general relativity. Einstein's theory rests on the basis that the speed of light is the same for every observer and that inertial and gravitating masses are the same. Ultimately this is thus also the reason why mass and energy curve the structure of spacetime.
Later it was understood that general relativity is (one of) the consequences of a Universe having so-called local Lorentz invariance. The details are a bit technical but basically this is saying that the laws of physics are the same everywhere in space and time.
You might ask, well, why does the Universe have local Lorentz invariance?
In that case, I am afraid, I do not know the answer, perhaps that in the future physics will offer us a deeper insight to the nature of reality.
What are black holes and how are they formed?
Black holes are created when in a Supernova-explosion or after a collision between two neutronstars (which are mini black holes). The star collapses and the gravity becomes stronger and stronger, dragging everything towards the center. In the end, the gravity becomes so strong that not even light can escape.
What is plotted on the horizontal axis of an H-R diagram?
If you mean a Hertzsprung-Russell Diagram, which plots stars color, temperature, and absolute magnitude (see related link), then it looks like color and spectral class (temperature) are plotted on horizontal, and Absolute Magnitude/Lumenoscity are plotted on the vertical.
Are nebulas in elliptical galaxies?
Because of their age, elliptical galaxies are believed to have older stars and less gas and dust in their insterstellar medium than other types of galaxies, and thus their nebulae are less common. However, nebulae are presumed to exist in almost all galaxies; and some recent observations hint that the central black holes of elliptical galaxies may tend to preserve interstellar gas by preventing it from cooling enough for star formation.
Why are cosmic rays harmful to living organisms?
Cosmic rays are harmful to living organisms because they are high-energy particles that can damage cells and DNA, increasing the risk of cancer and other health problems. They can penetrate through the atmosphere and into our bodies, causing ionization and mutations in cells. Prolonged exposure to cosmic rays can have detrimental effects on living organisms.
How long does it take to get to the other planets?
The time taken depends on the speed of the traveler. At the fastest speed possible, the speed of light, it would take about 5 minutes to get to Mercury at its closest approach. Neptune would take about 4 hours to reach.
At more realistic speeds, like that of the Voyager 2 probe which now moves at a comparatively poky speed of 15km/sec, it takes years to get to the outer planets. The probe was launched in 1977 and reached Neptune in 1989.
What is indicated by a shift of galaxy spectral line toward the red part of its spectrum?
In simplest terms, the shift of galactic spectral lines towards the red end of the spectrum would indicate simply that the galaxy in question is receding from the observer. This is an example of the Doppler effect, where the frequency is lowered (wavelengths become longer, and in this case energy of the photons is decreased) by the relative motion of the observer. The redshifting of galaxies in all directions became the primary evidence of an expanding universe (cosmological redshift). Because the expansion of the universe is fairly uniform in all directions, those galaxies that are most distant are receding the fastest and thus evidence the greatest amount of redshift.
By contrast, if a characteristic spectral line of a galaxy or other object shifted towards the blue end of the spectrum (shorter wavelengths), it would be traveling towards the observer.
What are the planets of Andromeda?
Because the Andromeda galaxy is so distant it is significantly difficult to identify planets in it - although there are likely hundreds of billions. Using a technique called gravitational microlensing, one planetary candidate within Andromeda has been announced by a team of scientists; the exoplanet is a stellar companion and thought to have about six or seven times the mass of Jupiter.
What was coperinicus's theory about the solar system?
The Copernican theory challenged the popular notion that the earth was at the center of the solar system, and instead proposed that the Sun was; ("Heliocentric") and indicated that observations of motions of other planets and stars was consistent with the Earth itself being the object that moved.
Where does the black hole send things to?
Black holes pull in objects with their strong gravitational pull, and those objects are sent into the singularity at the center of the black hole. It is believed that once objects pass the event horizon of a black hole, they are ultimately crushed into a single point of infinite density.
What was the first earthmade object to land on another celestial body?
The USSR initially led in space exploration in the 1950s and 60s, and after several failures managed to get the first object onto the moon in 1959 - Luna 2, although it was a crash more than a surface landing, and was followed by quite a list of other unmanned probes which crashed either intentionally or unintentionally. A proper landing didn't happen until Luna 9 landed on the surface in 1966. By then, the United States had already started crashing probes beginning with Ranger 4 in 1962, and after several others, a proper landing of Surveyor 1 in 1966. The Apollo missions famously got the first human to another celestial body, crashing the Apollo 10 descent stage onto the moon in 1969, then in that same year successfully landing the Apollo 11 lunar module allowing Armstrong and Aldrin to be the first people to walk on the surface of another celestial body.
How far is the sunflower galaxy?
The Sunflower Galaxy (M63, or NGC 5055) is a spiral galaxy in the constellation Cane.
It is approximately 37 million light years from us.
How long does it take for the milkyway galaxy to rotate 1 time?
The Milky Way galaxy takes about 200-250 million years to complete one full rotation. This rotation speed varies based on the distance from the center of the galaxy, with stars closer to the center orbiting faster than those further out.
Yes, planets form around stars. In order to be a planet, one of the requirements is that you have to orbit around a sun. Also, as far as physicists can tell, planets form in the dust of other stars that have already died and left their matter.
Why do planets go in an elipce?
All planets in the solar system have an elliptical orbit to some degree - Venus is the most circular or least elliptical. The imperfection in the circularity of the orbit is simply a reflection of the initial conditions of the planet's formation, if you consider the rotational inertia of the components of the accretion disk from which planets formed, it's almost certain that they will not have precisely the exact amount to form a circular orbit, there would always be a slight irregularity no matter how small.
The reason for the shape of the ellipse reflects this irregularity in terms of the gravitational force between the planet and the sun; laws of physics do the rest. You might say that because gravity's force follows an inverse-square law, the mathematics of a stable orbit are such that an ellipse is consequential. This same observation appears in other guises; Kepler's laws indicate that a line joining the planet to the sun sweeps out equal areas in equal times; when a planet is closer to the sun and feels more force it moves faster, further away, it moves more slowly.
Finally, note that the orbits' ellipses themselves also rotate around the sun (apsidal precession), making the actual orbit a complex-looking spiral shape; as if you had slightly rotated the entire ellipse about the focus that the sun occupies with each orbit. Newton made some calculations to explain this motion; Einstein refined this somewhat in general relativity.
What planet traps all the heat?
Venus is the planet that traps the most heat due to its thick atmosphere composed mainly of carbon dioxide. This greenhouse effect causes extremely high temperatures on the planet's surface, making it the hottest planet in our solar system.
What definition of planets did Pluto not have?
The much-debated 2006 reclassification of Pluto as a dwarf planet happened because of the newly agreed-upon threefold definition of a planet: it has to be in solar orbit, has to be spherical (or in hydrostatic equilibrium) and has to have cleared its orbit - and it failed on the third count, since Pluto was considered to have only cleared less than a tenth such mass.
What is a non-luminous and not a planet?
One might safely say that a turnip is neither luminous nor a planet - but given the astronomical context, it's a safe inference that the subject of interest would be celestial bodies. Some stellar remnants would qualify, one in particular being a black dwarf - which is basically a white dwarf that has cooled down through the brown dwarf phase to a point where it no longer emits radiation (per current calculations, the time taken for this to happen is very long indeed). Other candidates might be a neutron star, or a black hole - in both cases presuming luminosity excludes nearby effects such as highly energetic accretion disks or relativistic polar jets such as are found at active galactic nuclei or quasars (ironically, among the most luminous regions known). Other solar system objects which would qualify would include objects too small to be planets such as asteroids, or others that don't fit the planet definition (such as moons). Although most of these objects could reflect light, strictly speaking, they are not usually themselves luminous.
What is a galaxy made of and what are the different types?
Galaxies are made up of stars, typically in orbit around a central black hole. Our milky way has something around 200 or 300 billion stars. Galaxies also contain stellar remnants like white dwarfs, neutron stars, and stellar mass black holes; nebulae of gas and dust, and a very sparse interstellar medium containing small amounts of particles. Because of observations of anomalies in rotational velocities, galaxies are also assumed to contain significant amounts of non-visible or dark matter.
The stars themselves are made up mostly of lighter elements like hydrogen and helium, and heavier elements decreasing in fraction of the composition as the atomic number increases.
Galactic types are classified by their appearance, which falls into three main types, irregular, elliptical, and spiral. Spirals subdivide into barred and non-barred, although some evidence indicates bars may be temporary structures. The Hubble classification scheme assigns a short letter designation to the various types. Our own Milky Way is a barred spiral galaxy.
What is the last episode of Planet Sheen?
It does appear to be cancelled even though it hasn't been officially said but it did not appear on Nickelodeon's 2013 Upfronts so that's a strong indicator it's cancelled.
The last episode of Planet Sheen is Banana Quest. The plot being Sheen, Doopy & Assefa go on a quest to find a banana to make a sick Nesmith feel better.
How long it takes for the galaxy to orbit the univese?
The idea that the entire universe itself is spinning remains a question in astrophysics, and opposes the commonly accepted model that the universe is generally homogenous and isotropic - the same in all directions. Some studies hint that the universe itself may have a rotational motion but the concept has not gained general acceptance.
There are of course, orbital motions on smaller scales; rotations do seem to be part of a hierarchy ever increasing in scale; our sun taking about a fifth of a billion years to orbit the galactic center. It might be helpful to add that the galaxy is gravitationally bound to a group of galaxies forming a component of a larger scale galactic cluster which is in turn part of a supercluster; and these may be components of the largest scale structures known in the universe known as galactic filaments or walls; some of these structures appear to have intrinsic angular momentum around a common center of gravity, and, per laws of orbital mechanics, the further apart or bigger the structure, the slower it rotates.
How would earth react if it got sucked into a black hole?
First, this seems pretty unlikely for the foreseeable future -- there's no evidence of a full sized black hole anywhere near earth (Chandrasehkar's limit says neutron stars can't occur at less and 1.44 solar mass, and stellar black holes are believed to occur at no less than 3 solar masses, and possibly more).
Smaller, primordial black holes may (or may not) once have existed, but Stephen Hawking's work on Hawking Radiation shows that, the smaller the black hole, the more energy gets expelled, hence quantum black holes (tiny ones) are likely to "evaporate".
However, if we imagine that there was a black hole very near the earth, we'd first see tidal effects as the earth responded to the gravitational field of the stellar body. Depending on how far away the earth and our imaginary black hole are, we conceivably could go into a stable orbit around it (although, dependiing on the mass, the accretion disk of the black hole might well emit enough radiation to cook us). Farther in, the earth would eventually spiral into the Schwarzchild radius. Once i9nside the Schwarzchild radius, it is postualted we could (a) see the incoming light from another universe (whimsically named "elsewhere" because "you can't get there from here"). Also, some of Hawking's work hints that, while traval along the spatial axes would no longer be mutable (as they are here in n-space, where we can travel freely spatially, but only in one direction in time), temporal travel would, in a manner of speaking, be possible.
On the other hand, Einstein's concepts of relativity give us some real problems here, particularly time dilation. Briefly, the following assumptions are made (and so far have not been disproven):
- The effects of gravity are indistinguishable from accelleration.
- When viewed by an external observer, an object accellerating towrds the speed of light moves more slowly through time.
- And, from a relative observer's standpoint, that object accellerating towards the speed of light reaches c or light speed exactly an infinite number of years in the relative observer's future.
This implies that, if there was a black hole across the room from you (all other effects notwithstanding) and you fired a bullet into it, you would see the bullet slow and come to an apparent stop (relative to you), before it could cross the event horizon. This is because gravity and accelleration are indistinguishable, so the grvaity at the event horizon is equivalent to a lightspeed effect. This in turn means that, outside the black hole, one cannot observe matter passing the event horizon.
How this works in reality is a bit of a mystery. Of course, we cannot "see" a black hole -- nothing escapes the Schwarzchild radius, so cannot be "obseved". But gravitational effects outside the event horizon can be seen. And we observe the binary star, Cygnus X-1, and note that for two comparatively cool stars, that body is emmiting a huge amount of x-ray radiation. Coupling that with observations of eccentricities in X-1a and X-1b's orbits, we postulate the existing of a super-dense object of perhaps 10 solar masses, i.e. a black hole, As the black hole sucks in matter, friction heats, then superheats that matter, which forms an accretion disk as it falls into the black hole. So, we have a superhot, brightly glowing disk surrounding the black hole, as well as two stars that are sharing matter with each other and quite possibly the black hole too.
We see the xray radiation, which indicates the presence of an accretion disk, so we assume matter IS falling into the black hole.
So -- in answer to your question -- one possiblity is we enter the black hole, see the stars shining in elsewhere, and possibly travel in time, perhaps exiting the black hole an infinite number of years in the past -- or perhaps not. Also, there's the possibility that, due to Xeno's paradox, you'll never actually see anything go past the Schwarzchild radius.
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How and when did the planet earth form geologically?
The oldest rocks from space are dated back to about 4.5 billion years ago, so this is around when our planet would have formed. The entire Solar System (which includes the Earth) arose when a giant cloud of gas and dust called a nebula began to collapse under its own gravity. This probably happened when, about five billion years ago, a nearby star exploded in a supernova, releasing a shockwave that caused the cloud to contract. Most of the gas gathered in the center to form the Sun, while the rest flattened out into a spinning disk.
The heavier, metallic elements existed closer to the Sun and would form the terrestrial planets. Through gravity, dust particles within the protoplanetary disk began to stick together, growing into pebbles, then boulders, then planetesimals. These chunks of rock collided with one another and clumped together to form larger and larger bodies. This is called accretion: when an object grows in size and mass by gravitationally collecting the material around it. Slowly, over millions of years, Earth formed by this process.
Our planet started out as a hot mass of scorched rock. Volcanic outgassing created the early atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was still molten because of extreme volcanism and frequent collisions with other bodies. One very big collision is thought to have been responsible for creating the Moon and tilting the Earth at an angle. Over time, such cosmic bombardments ceased, allowing our planet to cool and form a solid crust. Water that was brought here by comets and asteroids condensed into clouds and the oceans took shape. Earth was finally hospitable to life, and the earliest forms that arose enriched the atmosphere with oxygen.
See the links below for more information.
Earth was formed by collisions within the giant disc-shaped cloud of material. Gravity gathered the dust and gas together into clumps.
Is there a planet called the goldilocks?
no, goldilocks is a zone around a star where a planet with appropriate atmospheric pressure can maintain the liquid water on its surface
Does absolute vacuum exist in a black hole?
Yes, the interior of a black hole is often described as a region of spacetime with extremely high gravitational forces, leading to densities beyond what we can comprehend. Within the event horizon, the vacuum would not be a traditional "empty space" as we conceptualize it, but instead a region where conventional physics breaks down.
