Stephen Hawking believes he knows how information escapes black holes

'... Basically, Hawking argues that the information about particles sucked into the hole sit on the surface of the event horizon as holograms (2D afterimages of a 3D object). "The idea is the super translations are a hologram of the ingoing particles," he told the crowd. "Thus they contain all the information that would otherwise be lost." What's more, that information can actually escape a black holes pull thanks to Hawking Radiation -- the concept that photons can sometimes be ejected from a black hole due to random quantum fluctuations.

These photons would carry the information off of the event horizon, however it wouldn't be of any use. "The information about ingoing particles is returned, but in a chaotic and useless form. This resolves the information paradox. For all practical purposes, the information is lost." Even if the information wasn't blasted into a parallel universe (which Hawking said is totally possible), it'd be like trying to read the data off a corrupted hard drive. Sure there's still "information" there, it's just not going to be of any use.

Oxymoronic Black Hole Provides Clues to Growth

A Sloan Digital Sky Survey image of RGG 118, a galaxy containing the smallest supermassive black hole ever detected. The inset is a Chandra image showing hot gas around the black hole.

Credits: NASA/CXC/Univ of Michigan/V.F.Baldassare, et al; Optical: SDSS

Astronomers using NASA’s Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile have identified the smallest supermassive black hole ever detected in the center of a galaxy. This oxymoronic object could provide clues to how larger black holes formed along with their host galaxies 13 billion years or more in the past.

Astronomers estimate this supermassive black hole is about 50,000 times the mass of the sun. This is less than half the mass of the previous smallest black hole at the center of a galaxy.

“It might sound contradictory, but finding such a small, large black hole is very important,” said Vivienne Baldassare of the University of Michigan in Ann Arbor, first author of a paper on these results published in The Astrophysical Journal Letters. “We can use observations of the lightest supermassive black holes to better understand how black holes of different sizes grow.”

The tiny heavyweight black hole is in the center of a dwarf disk galaxy, called RGG 118, located about 340 million light years from Earth, and was originally discovered using the Sloan Digital Sky Survey.

Researchers estimated the mass of the black hole by studying the motion of cool gas near the center of the galaxy using visible light data from the Clay Telescope. They used the Chandra data to figure out the X-ray brightness of hot gas swirling toward the black hole. They found the outward push of radiation pressure of this hot gas is about 1 percent of the black hole’s inward pull of gravity, matching the properties of other supermassive black holes.

Previously, scientists had noted a relationship between the mass of supermassive black holes and the range of velocities of stars in the center of their host galaxy. This relationship also holds for RGG 118 and its black hole.

“We found this little supermassive black hole behaves very much like its bigger, and in some cases much bigger, cousins,” said co-author Amy Reines of the University of Michigan. “This tells us black holes grow in a similar way no matter what their size.”

The black hole in RGG 118 is nearly 100 times less massive than the supermassive black hole found in the center of the Milky Way. It’s also about 200,000 times less massive than the heaviest black holes found in the centers of other galaxies.

Astronomers are trying to understand the formation of billion-solar-mass black holes from less than a billion years after the big bang, but many are undetectable with current technology. The black hole in RGG 118 gives astronomers an opportunity to study a nearby small supermassive black hole.

Astronomers think supermassive black holes may form when a large cloud of gas, with a mass of about 10,000 to 100,000 times that of the sun, collapses into a black hole. Many of these black hole seeds then merge to form much larger supermassive black holes. Alternately, a supermassive black hole seed could come from a giant star, about 100 times the sun’s mass, that ultimately forms into a black hole after it runs out of fuel and collapses.

“We have two main ideas for how these supermassive black holes are born,” said Elena Gallo of the University of Michigan. “This black hole in RGG 118 is serving as a proxy for those in the very early universe and ultimately may help us decide which of the two is right.”

Researchers will continue to look for other supermassive black holes that are comparable in size or even smaller than the one in RGG 118 to help decide which of the models is more accurate and refine their understanding of how these objects grow.

A preprint of these results is available online. The other co-author of the paper is Jenny Greene, from Princeton University in Princeton, New Jersey. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, manages Chandra's science and flight operations.

Meteors

NASA TV to Host Perseid Meteor Shower Program

Astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of Aug. 11 and early morning of Aug. 12, 2004 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. There are 51 Perseid meteors in the composite image, including one seen nearly head-on.

Credits: Fred Bruenjes

Thanks to a new moon, this week’s Perseid meteor shower is expected to be one of the best in years, and NASA Television will bring viewers a front row seat.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, will broadcast a live program about this year’s Perseid meteor shower from 10 p.m. EDT Wednesday, Aug. 12 to 2 a.m. Thursday, Aug. 13. The event will highlight the science behind the Perseids, as well as NASA research related to meteors and comets. The program will air on NASA TV and NASA’s UStream channel.

The Perseids have been observed for at least 2,000 years and are associated with the comet Swift-Tuttle, which orbits the sun once every 133 years. Every August, the Earth passes through a cloud of the comet’s orbital debris. This debris field -- mostly created hundreds of years ago -- consists of bits of ice and dust shed from the comet which burn up in Earth’s atmosphere to create one of the premier meteor showers of the year. 

The best opportunity to see the Perseid meteor shower is during the dark, pre-dawn hours of Aug. 13. The Perseids streak across the sky from many directions, with theoretical rates as high as 100 per hour. The last time the Perseids peak coincided with a new moon was in 2007, making this one of the best potential viewings in years.

Special guests on the live NASA TV broadcast include meteor experts Bill Cooke, Danielle Moser and Rhiannon Blaauw, all of NASA’s Meteoroid Environment Office, located at Marshall. They will provide on-air commentary, as well as answer questions online. Also scheduled to join the broadcast are experts from NASA’s Johnson Space Center in Houston, NASA’s Goddard Space Flight Center in Greenbelt, Maryland, NASA’s Ames Research Center in Moffett Field, California, the American Meteor Society and others.

Anyone can join in the conversation by tweeting questions to @NASA_Marshall with the hashtag #askNASA. Social media users may also post questions to Marshall’s Facebook page by replying to the Aug. 12 Perseid Q-and-A post.

Tropical Depression Molave (Northwest Pacific)

NASA Sees Tropical Depression Molave Spinning Down

On August 9 at 01:20 UTC (Aug. 8 at 9:20 p.m. EDT), NASA's Terra satellite captured a visible-light image of Tropical Depression Molave winding down about 400 miles away from Yokosuka, Japan.

Credits: NASA Goddard MODIS Rapid Response, Jeff Schmaltz

On August 8 at 12 a.m. EDT RapidScat saw strongest sustained winds in Molave's southeastern quadrant where wind speeds were near 24 meters per second (53.6 mph/86.4 kph), tropical-storm strength.

Credits: NASA JPL/Doug Tyler

NASA's Terra satellite and the RapidScat instrument both captured data on Tropical Depression Molave as it was spinning down in the Northwestern Pacific Ocean.

RapidScat is a NASA instrument that flies aboard the International Space Station and can measure sustained winds over an ocean surface. On August 8 at 4 p.m. UTC (12 a.m. EDT) RapidScat saw strongest sustained winds in Molave's southeastern quadrant where wind speeds were near 24 meters per second (53.6 mph/86.4 kph), tropical-storm strength. Since then, those winds have weakened.

On August 9 at 01:20 UTC (Aug. 8 at 9:20 p.m. EDT), the MODIS instrument aboard NASA's Terra satellite captured a visible-light image of Tropical Depression Molave winding down about 400 miles away from Yokosuka, Japan. The image showed a western quadrant devoid of clouds as vertical wind shear was pushing thunderstorms south and east of the center.

Two NASA centers created these images. The RapidScat image was created at NASA's Jet Propulsion Laboratory in Pasadena, California where the instrument is managed. The MODIS image was created by the NASA Goddard MODIS Rapid Response Team at NASA's Goddard Space Flight Center.

The Joint Typhoon Warning Center (JTWC) issued its final bulletin on Molave on August 9 at 1500 UTC (11 a.m. EDT). At that time, Molave had become a sub-tropical cyclone. It was centered near 28.6 North latitude and 140.6 East longitude, about 405 nautical miles (469.5 miles/755.6 km) south of Yokosuka, Japan. Molave was moving to the north at 8 knots (9.2 mph/14.8 kph) and had maximum sustained winds near 25 knots 28.7 mph/46.3 kph). 

By August 10 at 1500 UTC (11 a.m. EDT), the remnants of Molave were centered about 287 nautical miles (330.3 miles/531.5 km) south-southeast of Tokyo, Japan, near 31.0 North latitude and 141.2 East longitude. JTWC noted that the low pressure area remains well-defined, but has scattered thunderstorms and clouds pushed to the northeast of the center by wind shear. Precipitable water imagery shows cool dry air wrapping into the system from the south which will further help prevent thunderstorms from forming.

As NASA satellites and instruments continue to eye the low pressure area, the potential for Molave to re-develop in the next day is low.

Rob Gutro
NASA's Goddard Space Flight Center

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Aug. 07, 2015 - NASA Sees a Lop-sided Tropical Depression Molave Form

On Aug. 4, 2015, at 12:25 UTC (8:25 a.m. EDT) NASA's Terra satellite captured this infrared image of Tropical Depression Molave. The red and yellow colors indicate coldest temperatures.

Credits: NRL/NASA

The fifteenth tropical depression of the Northwestern Pacific typhoon season formed on August 7, 2015 as NASA's Terra passed overhead. The storm appears lop-sided, however, because wind shear pushed clouds north and northeast of its center.

On August 4 at 12:25 UTC (8:25 a.m. EDT) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Terra satellite captured an infrared image of Tropical Depression Molave. The strongest thunderstorms with the coldest cloud top temperatures (that were highest in the atmosphere) were north and northeast of the center of circulation. Molave also appeared to be elongated in the image.

The reason that the strongest thunderstorms are displaced from the center is because of moderate (20 to 25 knots) southerly vertical wind shear.

Tropical Depression Molave formed at 0900 UTC (5 a.m. EDT). By 1500 UTC (11 a.m. EDT), Molave was located near 23.9 North latitude and 146.7 East longitude, about 300 nautical miles (345 miles/555.6 km) east of Iwo To, Japan. It had maximum sustained winds near 30 knots (34.5 mph/55.5 kph) and was moving to the north-northwest at 15 knots (17.2 mph/27.7 kph).

The Joint Typhoon Warning Center forecast calls for the storm to move northwest and then turn to the northeast on August 9. Long term forecasts take the storm parallel to Japan while its center remains far from land.

Tropical Depression Molave (Northwest Pacific)

NASA Sees Tropical Depression Molave Spinning Down

On August 9 at 01:20 UTC (Aug. 8 at 9:20 p.m. EDT), NASA's Terra satellite captured a visible-light image of Tropical Depression Molave winding down about 400 miles away from Yokosuka, Japan.

Credits: NASA Goddard MODIS Rapid Response, Jeff Schmaltz

On August 8 at 12 a.m. EDT RapidScat saw strongest sustained winds in Molave's southeastern quadrant where wind speeds were near 24 meters per second (53.6 mph/86.4 kph), tropical-storm strength.

Credits: NASA JPL/Doug Tyler

NASA's Terra satellite and the RapidScat instrument both captured data on Tropical Depression Molave as it was spinning down in the Northwestern Pacific Ocean.

RapidScat is a NASA instrument that flies aboard the International Space Station and can measure sustained winds over an ocean surface. On August 8 at 4 p.m. UTC (12 a.m. EDT) RapidScat saw strongest sustained winds in Molave's southeastern quadrant where wind speeds were near 24 meters per second (53.6 mph/86.4 kph), tropical-storm strength. Since then, those winds have weakened.

On August 9 at 01:20 UTC (Aug. 8 at 9:20 p.m. EDT), the MODIS instrument aboard NASA's Terra satellite captured a visible-light image of Tropical Depression Molave winding down about 400 miles away from Yokosuka, Japan. The image showed a western quadrant devoid of clouds as vertical wind shear was pushing thunderstorms south and east of the center.

Two NASA centers created these images. The RapidScat image was created at NASA's Jet Propulsion Laboratory in Pasadena, California where the instrument is managed. The MODIS image was created by the NASA Goddard MODIS Rapid Response Team at NASA's Goddard Space Flight Center.

The Joint Typhoon Warning Center (JTWC) issued its final bulletin on Molave on August 9 at 1500 UTC (11 a.m. EDT). At that time, Molave had become a sub-tropical cyclone. It was centered near 28.6 North latitude and 140.6 East longitude, about 405 nautical miles (469.5 miles/755.6 km) south of Yokosuka, Japan. Molave was moving to the north at 8 knots (9.2 mph/14.8 kph) and had maximum sustained winds near 25 knots 28.7 mph/46.3 kph). 

By August 10 at 1500 UTC (11 a.m. EDT), the remnants of Molave were centered about 287 nautical miles (330.3 miles/531.5 km) south-southeast of Tokyo, Japan, near 31.0 North latitude and 141.2 East longitude. JTWC noted that the low pressure area remains well-defined, but has scattered thunderstorms and clouds pushed to the northeast of the center by wind shear. Precipitable water imagery shows cool dry air wrapping into the system from the south which will further help prevent thunderstorms from forming.

As NASA satellites and instruments continue to eye the low pressure area, the potential for Molave to re-develop in the next day is low.

Rob Gutro
NASA's Goddard Space Flight Center

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Aug. 07, 2015 - NASA Sees a Lop-sided Tropical Depression Molave Form

On Aug. 4, 2015, at 12:25 UTC (8:25 a.m. EDT) NASA's Terra satellite captured this infrared image of Tropical Depression Molave. The red and yellow colors indicate coldest temperatures.

Credits: NRL/NASA

The fifteenth tropical depression of the Northwestern Pacific typhoon season formed on August 7, 2015 as NASA's Terra passed overhead. The storm appears lop-sided, however, because wind shear pushed clouds north and northeast of its center.

On August 4 at 12:25 UTC (8:25 a.m. EDT) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Terra satellite captured an infrared image of Tropical Depression Molave. The strongest thunderstorms with the coldest cloud top temperatures (that were highest in the atmosphere) were north and northeast of the center of circulation. Molave also appeared to be elongated in the image.

The reason that the strongest thunderstorms are displaced from the center is because of moderate (20 to 25 knots) southerly vertical wind shear.

Tropical Depression Molave formed at 0900 UTC (5 a.m. EDT). By 1500 UTC (11 a.m. EDT), Molave was located near 23.9 North latitude and 146.7 East longitude, about 300 nautical miles (345 miles/555.6 km) east of Iwo To, Japan. It had maximum sustained winds near 30 knots (34.5 mph/55.5 kph) and was moving to the north-northwest at 15 knots (17.2 mph/27.7 kph).

The Joint Typhoon Warning Center forecast calls for the storm to move northwest and then turn to the northeast on August 9. Long term forecasts take the storm parallel to Japan while its center remains far from land.

What Is a Black Hole?

A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.

Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.

How Big Are Black Holes?
Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object.

Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way.

An artist's drawing shows the current view of the Milky Way galaxy. Scientific evidence shows that in the middle of the Milky Way is a supermassive black hole.

Credits: NASA/JPL-Caltech

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The largest black holes are called "supermassive." These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.

How Do Black Holes Form?
Scientists think the smallest black holes formed when the universe began.

Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.

Scientists think supermassive black holes were made at the same time as the galaxy they are in.

This image of the center of the Milky Way galaxy was taken by the Chandra X-ray Observatory.

Credits: NASA/CXC/MIT/F.K. Baganoff et al.

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If Black Holes Are "Black," How Do Scientists Know They Are There?
A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.

Could a Black Hole Destroy Earth?
Black holes do not go around in space eating stars, moons and planets. Earth will not fall into a black hole because no black hole is close enough to the solar system for Earth to do that.

Even if a black hole the same mass as the sun were to take the place of the sun, Earth still would not fall in. The black hole would have the same gravity as the sun. Earth and the other planets would orbit the black hole as they orbit the sun now.

Sagittarius A* is the black hole at the center of the Milky Way galaxy.

Credits: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

View Larger Image

The sun will never turn into a black hole. The sun is not a big enough star to make a black hole.

How Is NASA Studying Black Holes?
NASA is using satellites and telescopes that are traveling in space to learn more about black holes. These spacecraft help scientists answer questions about the universe.

Hubble Peers into the Most Crowded Place in the Milky Way

This NASA/ESA Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way. It is located about 25,000 light-years from Earth in the constellation of Sagittarius (The Archer), close to the heart of our galaxy, the Milky Way. It is, like its neighbor the Quintuplet Cluster, a fairly young astronomical object at between two and four million years old.

The Arches cluster is so dense that in a region with a radius equal to the distance between the sun and its nearest star there would be over 100,000 stars! At least 150 stars within the cluster are among the brightest ever discovered in the Milky Way. These stars are so bright and massive that they will burn their fuel within a short time (on a cosmological scale that means just a few million years). Then they will die in spectacular supernova explosions. Due to the short lifetime of the stars in the cluster the gas between the stars contains an unusually high amount of heavier elements, which were produced by earlier generations of stars.

Despite its brightness the Arches Cluster cannot be seen with the naked eye. The visible light from the cluster is completely obscured by gigantic clouds of dust in this region. To make the cluster visible astronomers have to use detectors which can collect light from the X-ray, infrared, and radio bands, as these wavelengths can pass through the dust clouds. This observation shows the Arches Cluster in the infrared and demonstrates the leap in Hubble’s performance since its 1999 image of same object.

Hubble Looks at Stunning Spiral

This little-known galaxy, officially named J04542829-6625280, but most often referred to as LEDA 89996, is a classic example of a spiral galaxy. The galaxy is much like our own galaxy, the Milky Way. The disk-shaped galaxy is seen face on, revealing the winding structure of the spiral arms. Dark patches in these spiral arms are in fact dust and gas — the raw materials for new stars. The many young stars that form in these regions make the spiral arms appear bright and bluish.

The galaxy sits in a vibrant area of the night sky within the constellation of Dorado (The Swordfish), and appears very close to the Large Magellanic Cloud  — one of the satellite galaxies of the Milky Way.

The observations were carried out with the high resolution channel of Hubble’s Advanced Camera for Surveys. 

Hubble

Hubble Finds a Little Gem

This colorful bubble is a planetary nebula called NGC 6818, also known as the Little Gem Nebula. It is located in the constellation of Sagittarius (The Archer), roughly 6,000 light-years away from us. The rich glow of the cloud is just over half a light-year across — humongous compared to its tiny central star — but still a little gem on a cosmic scale.

When stars like the sun enter "retirement," they shed their outer layers into space to create glowing clouds of gas called planetary nebulae. This ejection of mass is uneven, and planetary nebulae can have very complex shapes. NGC 6818 shows knotty filament-like structures and distinct layers of material, with a bright and enclosed central bubble surrounded by a larger, more diffuse cloud.

Scientists believe that the stellar wind from the central star propels the outflowing material, sculpting the elongated shape of NGC 6818. As this fast wind smashes through the slower-moving cloud it creates particularly bright blowouts at the bubble’s outer layers.

Hubble previously imaged this nebula back in 1997 with its Wide Field Planetary Camera 2, using a mix of filters that highlighted emission from ionized oxygen and hydrogen. This image, while from the same camera, uses different filters to reveal a different view of the nebula.  

Hubble

Stormy Seas in Sagittarius

Some of the most breathtaking views in the Universe are created by nebulae — hot, glowing clouds of gas. This new NASA/ESA Hubble Space Telescope image shows the center of the Lagoon Nebula, an object with a deceptively tranquil name, in the constellation of Sagittarius. The region is filled with intense winds from hot stars, churning funnels of gas, and energetic star formation, all embedded within an intricate haze of gas and pitch-dark dust.

News

Alien of the Deep Has Needle-Sharp Teeth & a Shiny Head Lure

A female of the newfound Lasiognathus dinema species from the Gulf of Mexico.

Lurking in the dark depths of the sea, a new species that looks more like an alien than a fish has been discovered, a creature with needlelike teeth and a glowing fishing pole of sorts atop its head.

Scientists spotted three females of the new species of anglerfishbetween 3,280 feet and nearly 5,000 feet (1,000 and 1,500 meters) beneath the Gulf of Mexico. The little fish, whose bodies ranged in length from 1.2 to 3.7 inches (30 to 95 millimeters), live under extreme conditions: No sunlight penetrates their deep habitats where they endure immense pressures of more than 2,200 pounds (1 ton) per square inch.

Now called Lasiognathus dinema, the anglerfish stood out from other species in its genus by the curved appendages jutting out from its so-called esca, or the organ at the tip of the "fishing rod" that contains light-producing bacteria. The species name dinema comes from the Greek words "di" for "two" and "nema" for "thread," referring to the threadlike extensions sprouting from the bases of the light organ's hooks, the researchers, Tracey Sutton of Nova Southeastern University in Florida and Theodore Pietsch of the University of Washington, write in the journal Copeia (published by the American Society of Ichthyologists and Herpetologists). 

News

The Internet Thinks NASA Has Photographed a Crab Monster on Mars

Image via NASA

NASA’s Mars Curiosity Rover has been rolling around the red planet, sending photos back to Earth. But people online reckon they have spotted a Martian crab monster in one of the photos.

Can you spot it?

Image via NASA

Zoom in a bit…

SOLAR STRUCTURE

Core

This is the inner most part of the Sun. Here gravity has squeezed the Sun so much that hydrogen compresses together to form helium and release energy through nuclear fusion. All the energy that comes away from the Sun and all the reaches the Earth started in the core. The core is around 150 times as dense as water and has a blazing temperature of around 15 million degrees Celsius or 28 million degrees Fahrenheit.

Radiative Zone

This is the layer of the Sun above the super dense core. The density slowly decreases moving away from the core. Light produced by nuclear fusion in the core travels out in the shell called the radiative zone. This layer is not as dense as the core but it is still so dense that light from the core bounces around taking about 100,000 years to move through the radiative zone.

Convection Zone

This is the layer of the Sun above the radiative zone. When the density of the radiative zone becomes low enough energy from the core in the form of light is converted into heat. Much like the bubbles in a pot of boiling, the heat from the edge of the radiative zone rises until it cools enough that it sinks back down. This pattern of heated material rising then cooling happens in big bubbles called convection cells.

Solar Atmosphere

• Photosphere

The material that reaches the top of the convection zone cools by giving of light. This region of the Sun is the first part of the Sun that is visible to us and we call it the photosphere. This is wear the light we see from the Sun originates. If we could look at the Sun directly (never stare at the Sun without the proper equipment) we would see the photosphere. Even though the layer is not solid we call this part of the Sun the surface and it is also were the solar atmosphere starts. Its temperature is around 5,800 Celsius or 10,000 degrees Fahrenheit.

• Chromosphere

Above the photosphere is a layer of the atmosphere about 2,000 km thick called the chromosphere. The temperature increases as you move higher to about 20,000 degrees Celsius at the top of the chromosphere. The chromosphere is no longer white light like the photosphere but is mostly red in visible light. It can be seen as red flashes during a total solar eclipse.

• Corona

The highest part of the solar atmosphere is called the corona. The corona starts around 10,000 km above the solar photosphere. Unlike the atmosphere of the Earth the atmosphere of the Sun continues to get hotter as you move away from the solar surface. The answer of why exactly this happens is one of the biggest questions of astronomy and solar physics of the 20th and 21st centuries. At 20,000-25,000 km away from the solar surface the corona has an average temperature of 1,000,000 to 2,000,000 million degrees Celsius. But the density is very low, about 1 billion times less dense than water.

Tutorial on sun

Sun:

The Sun is a self-luminous ball of gas held together by its own gravity and powered by thermonuclear fusion in its core. Our Sun is a typical star among the various stars in the Galaxy, average in mass, size and temperature. It is a ``dwarf'' star (compared to supergiant stars, see AST122 next term) with a radius of 109 Earth radii and a mass of 3.3x10⁵ Earth masses.

The Sun's lifetime is about 10 billion years, meaning that after this time the hydrogen in its core will be depleted. The Sun will then evolve into a red giant, consuming Mercury, Venus and the Earth in its expanded envelope. The Sun is currently 5 billion years old.

The most outstanding characteristic of the Sun is the fact that it emits huge quantities of electro-magnetic radiation of all wavelengths. The total output of the Sun is 3.99x10³³ ergs/sec. Only 1.8x10²⁴ ergs/sec strikes the Earth (since it is small in angular size), which is called the solar constant, but the amount of energy reaching the Earth in 30 mins is more than the power generated by all of human civilization. This energy is what powers the atmosphere and our oceans (storms, wind, currents, rainfall, etc.).

The energy emitted by the Sun is divided into 40% visible light, 50% IR, 9% UV and 1% x-ray, radio, etc. The light we see is emitted from the ``surface'' of the Sun, the photosphere. The Sun below the photosphere is opaque and hidden.

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Solar Structure:

The Sun is divided into six regions based on the physical characteristics of these regions. The boundaries are not sharp.

• fusion core - region of energy generation
• radiation shell - the region where energy transport is by radiation flow
• convection shell - the region where energy transport is by convection cells
• photosphere - the surface where photons are emitted
• chromosphere - the atmosphere of the Sun
• corona - the superhot region where the solar wind originates

The radii and temperatures of these regions are the following:

region                  radius        temperature
-------------------------------------------------
fusion core         0.3 solar radii     15x10^6 K
radiation shell   0.3-0.6 solar radii    6x10^6 K
convection shell  0.6-1.0 solar radii    1x10^6 K
photosphere             100 km             6000 K
chromosphere           2000 km           30,000 K
corona                 10^6 km           1x10^6 K

The Sun rotates differentially since it is not a solid. The solar equator completes one rotation in 25 days. The poles complete one rotation in 36 days.

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Sun's Interior:

Stars form from clouds of gas and collapse under self-gravity. The collapse is stopped by internal pressure in the core of the star. During the collapse, the potential energy of infalling hydrogen atoms is converted to kinetic energy, heating the core. As the temperature goes up, the pressure goes up to stop the collapse. The heat from the collapse is sufficient for the Sun to shine, but only for a timescale of 15 million years (called the Kelvin-Helmholtz time). Since the Sun is 5 billion years old, then it must be producing its own energy rather than shining on leftover energy from formation (like Jupiter).

The structure of the Sun is determined by 5 relations or physical concepts:

1. hydrostatic equilibrium - the fact that pressure balances the self-gravity
   
2. thermal equilibrium - the amount of energy generated equals the amount radiated away
   
3. opacity - the resistance of the solar envelope to the flow of photons (how fast the energy is released)
   
4. energy transport - how energy is transported from the core to the photosphere (convection or radiation)
   There are three ways to transfer energy; conduction, convection and radiation. Conduction, the collisional transfer of energy between atoms, only occurs between solids (such as a hot pan and your hand), so is not found in the Sun. Convection is the motion of heated material, such as bubbles in boiling water. Radiation is the transfer of energy by electromagnetic waves (light). Only convection and radiation transfer are important in the Sun and the opacity determines which method is used. When the temperature is high and all the atoms are stripped of their electrons, the opacity is low and radiation transfer is dominant.
   When the temperature drops, such as in the outer layers of the solar interior, the protons and electrons recombine to form atoms and the opacity goes up. High opacity slows the transfer of energy by radiation, so bubbles form. These bubbles are hot and low in density, thus starting a convective flow.
   
5. energy production - in the case of stars, energy is produced by thermonuclear fusion (see below)

These 5 relationships, described as mathematical formula, show how energy is generated, how that energy effects the structure of the Sun and how that energy is transported to the surface to make the Sun shine.

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Thermonuclear Fusion:

Energy generation is the heart of the solar process. Normally, particles with like charges (positive-positive or negative-negative) repel each other, this is called electrostatic repulsion. But at temperatures above 15x10⁶ K, the motions of protons are high enough to overcome the electrostatic forces and the nuclei can ``fuse''. Nuclear reactions involve many elementary particles that make up all of matter (this is called the Standard Model). The primary output from nuclear reactions are photons in the form of gamma-rays, but a large number of other particles are important as well.

This fusion reaction in the Sun is called the proton-proton chain (the same process that powers H-bombs). It has the following four stages:

All the gamma-rays in the core are scattered many, many times. Each scattering exchanges energy so that the photons convert into visible, UV, IR and radio photons, as well as high energy ones, producing a thermal spectrum.

There are several tests to a solar model produced from the about relationships:

1. Solar oscillations - the Sun is not in perfect balance (hydrostatic equilibrium) but oscillates with periods from 5 to 160 minutes. The details are similar to seismic waves and are used to investigate the density changes in the core.
2. Solar neutrinos - since the interact weakly with matter, solar neutrinos created during the proton-proton chain reactions are a direct look into the current reaction rates. Large underground neutrino detectors, such as the Super Kamiokande in Japan, are currently detecting less than a 1/3 of the number of neutrinos then what is predicted by the equations.