Neutron Stars

Neutron stars are compact objects that are created in the cores of massive stars during supernova explosions. The core of the star collapses, and crushes together every proton with a corresponding electron turning each electron-proton pair into a neutron. The neutrons, however, can often stop the collapse and remain as a neutron star.

Neutron stars are fascinating objects because they are the most dense objects known. They are only about 10 miles in diameter, yet they are more massive than the Sun. One sugar cube of neutron star material weighs about 100 million tons, which is about as much as a mountain.

Like their less massive counterparts, white dwarfs, the heavier a neutron star gets the smaller it gets. Imagine if a 10 pound bag of flour was smaller than a 5 pound bag!

Neutron stars can be observed occasionally, as with Puppis A above, as an extremely small and hot star within a supernova remnant. However, they are more likely to be seen when they are a pulsar or part of an X-ray binary.

source:http://imagine.gsfc.nasa.gov 

Neutron Stars and Pulsars

A neutron star is about 20 km in diameter and has the mass of about 1.4 times that of our Sun. This means that a neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons! Because of its small size and high density, a neutron star possesses a surface gravitational field about 2 x 10¹¹ times that of Earth. Neutron stars can also have magnetic fields a million times stronger than the strongest magnetic fields produced on Earth. Neutron stars are one of the possible ends for a star. They result from massive stars which have mass greater than 4 to 8 times that of our sun. After these stars have finished burning their nuclear fuel, they undergo a supernova explosion. This explosion blows off the outer layers of a star into a beautiful supernova remnant. The central region of the star collapses under gravity. It collapses so much that protons and electrons combine to form neutrons. Hence the name “neutron star”.

Neutron stars may appear in supernova remnants, as isolated objects, or in binary systems. Four neutron stars are thought to have planets. When a neutron star is in a binary system, astronomers are able to measure its mass. From a number of such binaries seen with radio or X-ray telescopes, neutron star masses has been found to be about 1.4 times the mass of the Sun. For binary systems containing an unknown object, this information helps distinguish whether the object is a neutron star or a black hole, since black holes are more massive than neutron stars.

What is a Pulsar and What Makes it Pulse?

Simply put, pulsars are rotating neutron stars. And pulsars pulse because they rotate!

A diagram of a pulsar, showing its rotation axis
and its magnetic axis

Pulsars were first discovered in late 1967 by graduate student Jocelyn Bell Burnell as radio sources that blink on and off at a constant frequency. Now we observe the brightest ones at almost every wavelength of light. Pulsars are spinning neutron stars that have jets of particles moving almost at the speed of light streaming out above their magnetic poles. These jets produce very powerful beams of light. For a similar reason that “true north” and “magnetic north” are different on Earth, the magnetic and rotational axes of a pulsar are also misaligned. Therefore, the beams of light from the jets sweep around as the pulsar rotates, just as the spotlight in a lighthouse does. Like a ship in the ocean that sees only regular flashes of light, we see pulsars turn on and off as the beam sweeps over the Earth. Neutron stars for which we see such pulses are called “pulsars”, or sometimes “spin-powered pulsars,” indicating that the source of energy is the rotation of the neutron star.

X-ray Observations of Pulsars

Some pulsars also emit X-rays. Below, we see the famous Crab Nebula, an undisputed example of a neutron star formed during a supernova explosion. The supernova itself was observed in 1054 A.D. These images are from the Einstein X-ray observatory. They show the diffuse emission of the Crab Nebula surrounding the bright pulsar in both the “on” and “off” states, i.e. when the magnetic pole is “in” and “out” of the line-of-sight from Earth.

Crab Pulsar “On”	Crab Pulsar “Off”

A very different type of pulsar is seen by X-ray telescopes in some X-ray binaries. In this case, a neutron star and a normal star form the binary system. The strong gravitational force from the neutron star pulls material from the normal star. The material is funneled onto the neutron star at its magnetic poles. In this process, called accretion, the material becomes so hot that it produces X-rays. The pulses of X-rays are seen when the hot spots on the spinning neutron star rotate through our line of sight from Earth. These pulsars are sometimes called “accretion-powered pulsars” to distinguish them from the spin-powered pulsars.

source:http://imagine.gsfc.nasa.gov 

Global Warming: An Inconvenient Truth

WHAT IS GLOBAL WARMING? Carbon dioxide and other gases warm the surface of the planet naturally by trapping solar heat in the atmosphere. This is a good thing because it keeps our planet habitable. However, by burning fossil fuels such as coal, gas and oil and clearing forests we have dramatically increased the amount of carbon dioxide in the Earth’s atmosphere and temperatures are rising.

The vast majority of scientists agree that global warming is real, it’s already happening and that it is the result of our activities and not a natural occurrence.¹ The evidence is overwhelming and undeniable.

We’re already seeing changes. Glaciers are melting, plants and animals are being forced from their habitat, and the number of severe storms and droughts is increasing.

	The number of Category 4 and 5 hurricanes has almost doubled in the last 30 years.2
	Malaria has spread to higher altitudes in places like the Colombian Andes, 7,000 feet above sea level.3
	The flow of ice from glaciers in Greenland has more than doubled over the past decade.4
	At least 279 species of plants and animals are already responding to global warming, moving closer to the poles.5

If the warming continues, we can expect catastrophic consequences.

	Deaths from global warming will double in just 25 years — to 300,000 people a year.6
	Global sea levels could rise by more than 20 feet with the loss of shelf ice in Greenland and Antarctica, devastating coastal areas worldwide.7
	Heat waves will be more frequent and more intense.
	Droughts and wildfires will occur more often.
	The Arctic Ocean could be ice free in summer by 2050.8
	More than a million species worldwide could be driven to extinction by 2050.9

There is no doubt we can solve this problem. In fact, we have a moral obligation to do so. Small changes to your daily routine can add up to big differences in helping to stop global warming. The time to come together to solve this problem is now – TAKE ACTION

¹ According to the Intergovernmental Panel on Climate Change (IPCC), this era of global warming “is unlikely to be entirely natural in origin” and “the balance of evidence suggests a discernible human influence of the global climate.”
² Emanuel, K. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436: 686-688.
³ World Health Organization
⁴ Krabill, W., E. Hanna, P. Huybrechts, W. Abdalati, J. Cappelen, B. Csatho, E. Frefick, S. Manizade, C. Martin, J, Sonntag, R. Swift, R. Thomas and J. Yungel. 2004. Greenland Ice Sheet: Increased coastal thinning. Geophysical Research Letters 31.
⁵ Nature.
⁶ World Health Organization
⁷ Washington Post, “Debate on Climate Shifts to Issue of Irreparable Change,” Juliet Eilperin, January 29, 2006, Page A1.
⁸ Arctic Climate Impact Assessment. 2004. Impacts of a Warming Arctic. Cambridge, UK: Cambridge University Press. Also quoted in Time Magazine, Vicious Cycles, Missy Adams, March 26, 2006.
⁹ Time Magazine, Feeling the Heat, David Bjerklie, March 26, 2006.

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Global Warming

Global Warming

Global warming is an increase in the average temperature of Earth’s surface. Since the late 1800’s, the global average temperature has increased about 0.7 to 1.4 degrees F (0.4 to 0.8 degrees C). Many experts estimate that the average temperature will rise an additional 2.5 to 10.4 degrees F (1.4 to 5.8 degrees C) by 2100. That rate of increase would be much larger than most past rates of increase.

Scientists worry that human societies and natural ecosystems might not adapt to rapid climate changes. An ecosystem consists of the living organisms and physical environment in a particular area. Global warming could cause much harm, so countries throughout the world drafted an agreement called the Kyoto Protocol to help limit it.

Causes of global warming

Climatologists (scientists who study climate) have analyzed the global warming that has occurred since the late 1800’s. A majority of climatologists have concluded that human activities are responsible for most of the warming. Human activities contribute to global warming by enhancing Earth’s natural greenhouse effect. The greenhouse effect warms Earth’s surface through a complex process involving sunlight, gases, and particles in the atmosphere. Gases that trap heat in the atmosphere are known as greenhouse gases.

The main human activities that contribute to global warming are the burning of fossil fuels (coal, oil, and natural gas) and the clearing of land. Most of the burning occurs in automobiles, in factories, and in electric power plants that provide energy for houses and office buildings. The burning of fossil fuels creates carbon dioxide, whose chemical formula is CO2. CO2 is a greenhouse gas that slows the escape of heat into space. Trees and other plants remove CO2 from the air during photosynthesis, the process they use to produce food. The clearing of land contributes to the buildup of CO2 by reducing the rate at which the gas is removed from the atmosphere or by the decomposition of dead vegetation.

A small number of scientists argue that the increase in greenhouse gases has not made a measurable difference in the temperature. They say that natural processes could have caused global warming. Those processes include increases in the energy emitted (given off) by the sun. But the vast majority of climatologists believe that increases in the sun’s energy have contributed only slightly to recent warming.

The impact of global warming

Thousands of icebergs float off the coast of the Antarctic Peninsula after 1,250 square miles (3,240 square kilometers) of the Larsen B ice shelf disintegrated in 2002. The area of the ice was larger than the state of Rhode Island or the nation of Luxembourg. Antarctic ice shelves have been shrinking since the early 1970’s because of climate warming in the region. Image credit: NASA/Earth Observatory

Continued global warming could have many damaging effects. It might harm plants and animals that live in the sea. It could also force animals and plants on land to move to new habitats. Weather patterns could change, causing flooding, drought, and an increase in damaging storms. Global warming could melt enough polar ice to raise the sea level. In certain parts of the world, human disease could spread, and crop yields could decline.

Harm to ocean life

Through global warming, the surface waters of the oceans could become warmer, increasing the stress on ocean ecosystems, such as coral reefs. High water temperatures can cause a damaging process called coral bleaching. When corals bleach, they expel the algae that give them their color and nourishment. The corals turn white and, unless the water temperature cools, they die. Added warmth also helps spread diseases that affect sea creatures.

Changes of habitat

Widespread shifts might occur in the natural habitats of animals and plants. Many species would have difficulty surviving in the regions they now inhabit. For example, many flowering plants will not bloom without a sufficient period of winter cold. And human occupation has altered the landscape in ways that would make new habitats hard to reach or unavailable altogether.

Weather damage

Extreme weather conditions might become more frequent and therefore more damaging. Changes in rainfall patterns could increase both flooding and drought in some areas. More hurricanes and other tropical storms might occur, and they could become more powerful.

Rising sea level

Continued global warming might, over centuries, melt large amounts of ice from a vast sheet that covers most of West Antarctica. As a result, the sea level would rise throughout the world. Many coastal areas would experience flooding, erosion, a loss of wetlands, and an entry of seawater into freshwater areas. High sea levels would submerge some coastal cities, small island nations, and other inhabited regions.

Threats to human health

Tropical diseases, such as malaria and dengue, might spread to larger regions. Longer-lasting and more intense heat waves could cause more deaths and illnesses. Floods and droughts could increase hunger and malnutrition.

Changes in crop yields

Canada and parts of Russia might benefit from an increase in crop yields. But any increases in yields could be more than offset by decreases caused by drought and higher temperatures — particularly if the amount of warming were more than a few degrees Celsius. Yields in the tropics might fall disastrously because temperatures there are already almost as high as many crop plants can tolerate.

Limited global warming

Climatologists are studying ways to limit global warming. Two key methods would be (1) limiting CO2 emissions and (2) carbon sequestration — either preventing carbon dioxide from entering the atmosphere or removing CO2 already there.

Limiting CO2 emissions

Two effective techniques for limiting CO2 emissions would be (1) to replace fossil fuels with energy sources that do not emit CO2, and (2) to use fossil fuels more efficiently.

Alternative energy sources that do not emit CO2 include the wind, sunlight, nuclear energy, and underground steam. Devices known as wind turbines can convert wind energy to electric energy. Solar cells can convert sunlight to electric energy, and various devices can convert solar energy to useful heat. Geothermal power plants convert energy in underground steam to electric energy.

Alternative sources of energy are more expensive to use than fossil fuels. However, increased research into their use would almost certainly reduce their cost.

Carbon sequestration could take two forms: (1) underground or underwater storage and (2) storage in living plants.

Underground or underwater storage would involve injecting industrial emissions of CO2 into underground geologic formations or the ocean. Suitable underground formations include natural reservoirs of oil and gas from which most of the oil or gas has been removed. Pumping CO2 into a reservoir would have the added benefit of making it easier to remove the remaining oil or gas. The value of that product could offset the cost of sequestration. Deep deposits of salt or coal could also be suitable.

The oceans could store much CO2. However, scientists have not yet determined the environmental impacts of using the ocean for carbon sequestration.

Storage in living plants

Green plants absorb CO2 from the atmosphere as they grow. They combine carbon from CO2 with hydrogen to make simple sugars, which they store in their tissues. After plants die, their bodies decay and release CO2. Ecosystems with abundant plant life, such as forests and even cropland, could tie up much carbon. However, future generations of people would have to keep the ecosystems intact. Otherwise, the sequestered carbon would re-enter the atmosphere as CO2.

Agreement on global warming

Delegates from more than 160 countries met in Kyoto, Japan, in 1997 to draft the agreement that became known as the Kyoto Protocol. That agreement calls for decreases in the emissions of greenhouse gases.

Emissions targets

Thirty-eight industrialized nations would have to restrict their emissions of CO2 and five other greenhouse gases. The restrictions would occur from 2008 through 2012. Different countries would have different emissions targets. As a whole, the 38 countries would restrict their emissions to a yearly average of about 95 percent of their 1990 emissions. The agreement does not place restrictions on developing countries. But it encourages the industrialized nations to cooperate in helping developing countries limit emissions voluntarily.

Industrialized nations could also buy or sell emission reduction units. Suppose an industrialized nation cut its emissions more than was required by the agreement. That country could sell other industrialized nations emission reduction units allowing those nations to emit the amount equal to the excess it had cut.

Several other programs could also help an industrialized nation earn credit toward its target. For example, the nation might help a developing country reduce emissions by replacing fossil fuels in some applications.

Approving the agreement

The protocol would take effect as a treaty if (1) at least 55 countries ratified (formally approved) it, and (2) the industrialized countries ratifying the protocol had CO2 emissions in 1990 that equaled at least 55 percent of the emissions of all 38 industrialized countries in 1990.

In 2001, the United States rejected the Kyoto Protocol. President George W. Bush said that the agreement could harm the U.S. economy. But he declared that the United States would work with other countries to limit global warming. Other countries, most notably the members of the European Union, agreed to continue with the agreement without United States participation.

By 2004, more than 100 countries, including nearly all the countries classified as industrialized under the protocol, had ratified the agreement. However, the agreement required ratification by Russia or the United States to go into effect. Russia ratified the protocol in November 2004. The treaty was to come into force in February 2005.

Analyzing global warming

Scientists use information from several sources to analyze global warming that occurred before people began to use thermometers. Those sources include tree rings, cores (cylindrical samples) of ice drilled from Antarctica and Greenland, and cores drilled out of sediments in oceans. Information from these sources indicates that the temperature increase of the 1900’s was probably the largest in the last 1,000 years.

Computers help climatologists analyze past climate changes and predict future changes. First, a scientist programs a computer with a set of mathematical equations known as a climate model. The equations describe how various factors, such as the amount of CO2 in the atmosphere, affect the temperature of Earth’s surface. Next, the scientist enters data representing the values of those factors at a certain time. He or she then runs the program, and the computer describes how the temperature would vary. A computer’s representation of changing climatic conditions is known as a climate simulation.

In 2001, the Intergovernmental Panel on Climate Change (IPCC), a group sponsored by the United Nations (UN), published results of climate simulations in a report on global warming. Climatologists used three simulations to determine whether natural variations in climate produced the warming of the past 100 years. The first simulation took into account both natural processes and human activities that affect the climate. The second simulation took into account only the natural processes, and the third only the human activities.

The climatologists then compared the temperatures predicted by the three simulations with the actual temperatures recorded by thermometers. Only the first simulation, which took into account both natural processes and human activities, produced results that corresponded closely to the recorded temperatures.

The IPCC also published results of simulations that predicted temperatures until 2100. The different simulations took into account the same natural processes but different patterns of human activity. For example, scenarios differed in the amounts of CO2 that would enter the atmosphere due to human activities.

The simulations showed that there can be no “quick fix” to the problem of global warming. Even if all emissions of greenhouse gases were to cease immediately, the temperature would continue to increase after 2100 because of the greenhouse gases already in the atmosphere. Contributors: Michael D. Mastrandrea, B.S., Graduate Fellow, School of Earth Sciences, Geological and Environmental Sciences, Stanford University. Stephen H. Schneider, Ph.D., Professor of Biological Sciences, Stanford University.

source:http://www.nasa.gov

Stars

Protostars Bright Stars Red Giants White Dwarfs

Birth of a Star

Protostars are stars that are about to be born. These are glowing clouds of interstellar gas and dust, which look like dark spots in the midst of light. Gravity causes every atom and every bit of dust to pull on every other one and all move to the center, causing the protostar to collapse. Having begun with a diameter of perhaps 1.5 trillion km, the protostar now shrinks at a very fast rate about 1,000 years, to a diameter of about 80 million km. Because the atoms move faster and faster as they fall toward the center, friction is created as they rub together and the temperature rises. The protostar starts at a temperature of about 100 K and over 1.000 years, rises to about 4,250 K. This heat causes the protostar to glow in with its own light, giving off even more light than our Sun even though it is not nearly as hot. After about 10,000 years, the protostar’s surface temperature is up to about 4,500 K and it is now 100 times as luminous as the Sun; after another 100,000 years the temperature is 5,000 K even though the protostar has been shrinking the entire time and only gives off about 10 times the light of the Sun. There is little change in temperature over the next 10 million years but the brightness continues to drop as the protostar contracts. The next 20 million years is the last stage of the protostar’s development where it equals the Sun in luminosity and its size becomes fixed at about 1.6 million km in diameter. 30 million years after the pocket of gas began to form, a star is born.

Bright Stars

A star has is born when a protostar stops shrinking in size. At this moment the core temperature reaches 10 million K and a reaction, called nuclear fusion begins in the core. Nuclear fusion is the joining, or fusing, of small atomic nuclei to create larger ones. The nuclei of two hydrogen atoms join to form the nucleus of one helium atom and there is a great release of energy. We see and feel this energy in the form of light and heat from the Sun; all other stars give off the same energy but they are too far away for us to observe it. The fusion in a star continues for about 90 percent of its life, but cannot go on forever. Our Sun is expected to continue this way for just over another 5 billion years. The life cycle of a star can be compared to a human life: the 30 million years as a protostar is like infancy or early childhood, from birth to about age 4. The 10 billion year period of nuclear fusion as a bright star is the time of youth and maturity, from age 4 to 76. Last is old age. But while humans tend to grow smaller, the star grows larger. It also becomes red in colour and for these reasons is called a red giant. Red Giants

Without the outward flow of energy from the star’s core, gravity now takes over, squeezing and compressing the core making it grow much smaller. The core radiates heat until it reaches about 4 million K; it is now releasing great amounts of energy which carries immense amounts of hydrogen gas out to the surface. The star begins to grow larger, however, it does not become brighter. As a result of a temperature drop, the star now glows red instead of blue-white. Astronomers have located a number of red giants in the universe. Alderbaran is in the constellation Taurus, Antares in Scorpio, Arcturus in Bootes, and Betelgeuse in Orion. Most of the red giants are found in globular clusters, which are groups of up to one million stars that move together through space. Astronomers believe that the main source of carbon and oxygen in the universe is the very hot cores of red giants and these elements make like as we know it possible.

Two globular clusters in the universe

White Dwarfs

As the star cools off, a cycle begins. As a result of the temperature drop, the outer gas layer spreads out; this causes the temperature to drop further, and this in turn causes the gas to spread farther. It eventually spreads to far that it actually separates from the body of the star altogether. A cloud of glowing atoms moves out in all directions; this is called a planetary nebula.

Planetary Nebula: “Hubble 5″

It is called such because early astronomers believed it looked like a distant planet. Today we know that a planetary nebula has nothing to do with a planet, but still the name remains. The gas particles eventually mix with the clouds of gas normally found between the stars and the planetary nebula disappears. All that now remains of the star is the central core which, because it is no longer giving off energy, begins to collapse bit by bit. This process can be compared to squishing a large closetfull of clothes into a small suitcase. The clothes are still the same, they just take up much less room. Likewise, all the matter that was in the large star is still there, only now is is packed much more tightly. This occurs until the star is about the same size as planet Earth. Astronomers guess that a teaspoon of this matter weighs about 907 metric tonnes! The star is still very hot, so hot that it gives off a white light and thus is called a white dwarf. With the passage of billions of years the white dwarf cools off, from white hot to yellow, and then red, eventually becoming completely cold and black. Astronomers have located about 500 hundred white dwarfs and of the 20 stars closest to Earth, 2 are white dwarfs.

White dwarf stars in globular cluster M4.

Home Constellations

Terrestrial Planets Gaseous Planets

Comets Asteroids The Sun

Protostars

Protostars are stars that are about to be born. These are glowing clouds of interstellar gas and dust, which look like dark spots in the midst of light. Gravity causes every atom and every bit of dust to pull on every other one and all move to the center, causing the protostar to collapse. Having begun with a diameter of perhaps 1.5 trillion km, the protostar now shrinks at a very fast rate about 1,000 years, to a diameter of about 80 million km. Because the atoms move faster and faster as they fall toward the center, friction is created as they rub together and the temperature rises. The protostar starts at a temperature of about 100 K and over 1.000 years, rises to about 4,250 K. This heat causes the protostar to glow in with its own light, giving off even more light than our Sun even though it is not nearly as hot. After about 10,000 years, the protostar’s surface temperature is up to about 4,500 K and it is now 100 times as luminous as the Sun; after another 100,000 years the temperature is 5,000 K even though the protostar has been shrinking the entire time and only gives off about 10 times the light of the Sun. There is little change in temperature over the next 10 million years but the brightness continues to drop as the protostar contracts. The next 20 million years is the last stage of the protostar’s development where it equals the Sun in luminosity and its size becomes fixed at about 1.6 million km in diameter. 30 million years after the pocket of gas began to form, a star is born.

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