Earth Like Planet Gliese 581c

Gliese 581c is a “super-earth” extrasolar planet orbiting the red dwarf star Gliese 581. It appears to be the first terrestrial extrasolar planet discovered in the hypothetical habitable zone surrounding its star, where surface temperatures might maintain liquid water and therefore be suitable for life as known on Earth. The planet is astronomically close, at 20.4 light years (193 trillion km or 119 trillion miles) from Earth in the direction of the constellation of Libra. Its star is identified as Gliese 581 by its number in the Gliese Catalogue of Nearby Stars; it is the 87th closest star system to the Sun that we know of.

Gliese 581c is the first extrasolar planet believed to possibly have a surface temperature similar to that of Earth. Assuming the planet’s mass is close to the lower limit determined by radial velocity measurements (the true mass is unknown), it would be the smallest known extrasolar planet around a main sequence star to date.

Discovery
The discovery of the planet by the team of Stéphane Udry University of Geneva’s Observatory in Switzerland was announced on April 24, 2007. The team used the HARPS instrument (an echelle spectrograph) on the European Southern Observatory 3.6 m Telescope in La Silla, Chile. The team employed the radial velocity technique to identify the planet. The Canadian-built MOST space telescope was used to conduct a follow-up study over the next six weeks. No transit was detected over this time, so a direct measurement of the planet has not yet been possible; however, the star’s apparent magnitude changed very little, indicating that it provides a stable source of light and heat to Gliese 581c.

The team released a paper dated April 27, 2007, published in the July, 2007 journal Astronomy and Astrophysics. In the paper they also announced the discovery of another planet in the system, Gliese 581d, with a minimum mass of 7.7 Earth masses and a semi-major axis of 0.25 astronomical units.

Mass
The existence of Gliese 581c and its mass have been measured by the Radial Velocity Method or the “wobble” method of detecting exoplanets. The mass of a planet is calculated by the small periodic movements around a common centre of mass between the host star Gliese 581 and its planets. Because the “wobbling” of Gliese 581 is a result of all planets in its system, the calculation of the mass of Gliese 581c depends on the presence of other planets in the Gliese 581 system and on the inclination of the orbital plane with respect to Earth. Using the known minimum mass of the previously detected Gliese 581b, and assuming the existence of Gliese 581d, Gliese 581c has a mass at least 5.03 times that of Earth. The mass of the planet cannot be very much larger than this or the system would be dynamically unstable.

Radius
If it is a rocky planet with a large iron core, Gliese 581c has a radius approximately 50% larger than that of Earth, according to Udry’s team. Gravity on such a planet’s surface would be approximately 2.24 times as strong as on Earth. If Gliese 581c is an icy and/or watery planet, its radius would be less than 2 times that of Earth, even with a very large outer hydrosphere, according to density models compiled by Diana Valencia and her team for Gliese 876d Gravity on the surface of such an icy and/or watery planet would be at least 1.25 times as strong as on Earth.

It is not possible to measure the radius of an exoplanet using Radial Velocity. The real value may be anything between the two extremes calculated by density models outlined above. If the planet transits the star as seen from our direction, the radius should be measurable, although with some uncertainty. Udry’s team intends to use the Canadian-built MOST space telescope to look for a transit of the planet in front of its host star. A transit measurement could very well determine whether Gliese 581 c is a primarily rocky or watery object, however, most exosolar planets do not transit their host star from Earth’s perspective.

Age
The Gliese 581 system is estimated to be around 4.3 billion years old. By comparison, the Solar System is estimated to be 4.57 billion years old.

Orbit
Gliese 581c has an orbital period (“year”) of 13 Earth days and its orbital radius is only about 7% that of the Earth, about 11 million km, while the Earth is 150 million kilometres from the Sun. Since the host star is smaller and colder than the Sun—and thus less luminous—this distance places the planet on the “warm” edge of the habitable zone around the star according to Udry’s team. A typical radius for an M0 star of Gliese 581′s age and metallicity is 0.00128 AU, against the sun’s 0.00465 AU. This proximity means that the primary star should appear 3.75 times wider and 14 times larger in area for an observer on the planet’s surface looking at the sky than the Sun appears to be from Earth’s surface.

Temperature
Using the measured stellar luminosity of Gliese 581 of 0.013 times that of our Sun, it is possible to calculate Gliese 581c’s equilibrium surface temperature, which does not take into account a possible atmosphere. According to Udry’s team, the equilibrium temperature for Gliese 581 c is −3° C / 26.6° F, assuming an albedo (reflectivity) such as Venus’ (0.64) and 40°C / 104° F for an Earth-like albedo (0.35).[8][2] The actual temperature on the surface also depends on the planet’s atmosphere, which remains unknown. Xavier Delfosse of the research team expects that the actual surface temperatures will be hotter; for instance, the corresponding calculation for Earth yields an “effective surface temperature” of 256 K/−17 °C/− 28°F, yet Earth’s true surface is 32 K warmer (an average of 288 K/15 °C/59°F) due to the greenhouse effect. Gliese 581 c receives more irradiance (3340 W/m2) from its star than Venus does (2620 W/m2) from our sun.

Liquid water
Gliese 581c is within the habitable zone where water—a necessary ingredient for life as we know it—could exist.[3][16] However, no direct evidence has been found. Techniques like the one used to measure HD 209458 b could be used to determine the presence of water vapor in an extrasolar planet’s atmosphere, but only in the rare case of a planet with an orbit aligned so as to transit its star, which Gliese 581c is not known to do.

Source: wikipedia.org

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Black Holes in the Universe

 

What is a black hole?  

A black hole is an object that is so compact (in other words, has enough mass in a small enough volume) that its gravitational force is strong enough to prevent light or anything else from escaping. 

  

The existence of black holes was first proposed in the 18th century, based on the known laws of gravity. The more massive an object, or the smaller its size, the larger the gravitational force felt on its surface. John Michell and Pierre-Simon Laplace both independently argued that if an object were either extremely massive or extremely small, it might not be possible at all to escape its gravity. Even light could be forever captured.  

The name “black hole” was introduced by John Archibald Wheeler in 1967. It stuck, and has even become a common term for any type of mysterious bottomless pit. Physicists and mathematicians have found that space and time near black holes have many unusual properties. Because of this, black holes have become a favorite topic for science fiction writers. However, black holes are not fiction. They form whenever massive but otherwise normal stars die. We cannot see black holes, but we can detect material falling into black holes and being attracted by black holes. In this way, astronomers have identified and measured the mass of many black holes in the Universe through careful observations of the sky. We now know that our Universe is quite literally filled with billions of black holes.  

Do Black Holes Obey the Laws of Gravity?

  Black holes obey all laws of physics, including the laws of gravity. Their remarkable properties are in fact a direct consequence of gravity.  

In 1687, Isaac Newton showed that all objects in the Universe attract each other through gravity. Gravity is actually one of the weakest forces known to physics. In our daily life, other forces from electricity, magnetism, or pressure often exert a stronger influence. However, gravity shapes our Universe because it makes itself felt over large distances. For example, Newton showed that his laws of gravity can explain the observed motions of the moons and planets in the Solar System.  

Albert Einstein refined our knowledge of gravity through his theory of general relativity. He first showed, based on the fact that light moves at a fixed speed (671 million miles per hour), that space and time must be connected. Then in 1915, he showed that massive objects distort the four-dimensional space-time continuum, and that it is this distortion that we perceive as gravity. Einstein’s predictions have now been tested and verified through many different experiments. For relatively weak gravitational fields, such as those here on Earth, the predictions of Einstein’s and Newton’s theories are nearly identical. But for very strong gravitational fields, such as those encountered near black holes, Einstein’s theory predicts many fascinating new phenomena.  

How big is a black hole?

  All matter in a black hole is squeezed into a region of infinitely small volume, called the central singularity. The event horizon is an imaginary sphere that measures how close to the singularity you can safely get. Once you have passed the event horizon, it becomes impossible to escape: you will be drawn in by the black hole’s gravitational pull and squashed into the singularity.  

The size of the event horizon (called the Schwarzschild radius, after the German physicist who discovered it while fighting in the first World War) is proportional to the mass of the black hole. Astronomers have found black holes with event horizons ranging from 6 miles to the size of our solar system. But in principle, black holes can exist with even smaller or larger horizons. By comparison, the Schwarzschild radius of the Earth is about the size of a marble. This is how much you would have to compress the Earth to turn it into a black hole. A black hole doesn’t have to be very massive, but it does need to be very compact!  

Some black holes spin around an axis, and their situation is more complicated. The surrounding space is then dragged around, creating a cosmic whirlpool. The singularity is an infinitely thin ring instead of a point. The event horizon is composed of two, instead of one, imaginary spheres. And there is a region called the ergosphere, bounded by the static limit, where you are forced to rotate in the same sense as the black hole although you can still escape.  

What types of black holes are there?

  Black holes often look very different from each other. But this is because of variety in what happens in their surroundings. The black holes themselves are all identical, except for three characteristic properties: the mass of the black hole (how much stuff it is made of), its spin (whether and how fast it rotates around an axis), and its electric charge. Amazingly, black holes completely erase all of the other complex properties of the objects that they swallow.  

Astronomers can measure the mass of black holes by studying the material that orbits around them. So far, we have found two types of black holes: stellar-mass (just a few times heavier than our Sun) or supermassive (about as heavy as a small galaxy). But black holes might exist in other mass ranges as well. For example, recent observations suggest there may be black holes with masses between stellar-mass and supermassive black holes.  

Black holes can spin around an axis, although the rotation speed cannot exceed some limit. Astronomers think that many black hole in the Universe probably do spin, because the objects from which black holes form (stars for example) generally rotate as well. Observations are starting to shed some light on this issue, but no consensus has so far emerged. Black holes could also be electrically charged. However, they would then rapidly neutralize that charge by attracting and swallowing material of opposite polarity. So astronomers believe that all black holes in the Universe are uncharged.  

Can a black hole bend light rays?

  Imagine that you are in orbit around a black hole at a safe distance outside the event horizon. What would the sky look like? Normally you would just see the background stars steadily sliding by, due to your own orbital motion. But the gravitational force of a black hole changes things considerably.  

Light rays that pass close to the black hole get caught and cannot escape. Therefore, the region around the black hole is a dark disk. Light rays that pass a little further away don’t get caught but do get bent by the black hole’s gravity. This makes the starfield appear distorted, as in a funhouse mirror. It also produces multiple images. You would see two duplicate images of the same star on opposite sides of the black hole, because light rays passing the black hole on either side get bent toward you. In fact, there are infinitely many images of each star, corresponding to light rays that circle the black hole several times before coming toward you.  

Einstein’s theory of general relativity predicts that every object bends light rays through its gravity. This is called gravitational lensing. For our Sun this effect is very weak, but it has been measured. For more massive and distant objects in the Universe much stronger lensing has been seen. However, it has not yet been possible to observe this effect near a black hole, or to directly photograph the dark disk surrounding a black hole. However, this may become possible in the foreseeable future.  

What happens when black holes collide?

  It is possible for two black holes to collide. Once they come so close that they cannot escape each other’s gravity, they will merge to become one bigger black hole. Such an event would be extremely violent. Even when simulating this event on powerful computers, we cannot fully understand it. However, we do know that a black hole merger would produce tremendous energy and send massive ripples through the space-time fabric of the Universe. These ripples are called gravitational waves.  

Nobody has witnessed a collision of black holes yet. However, there are many black holes in the Universe and it is not preposterous to assume that they might collide. In fact, we know of galaxies in which two supermassive black holes move dangerously close to each other. Theoretical models predict that these black holes will spiral toward each other until they eventually collide.  

Gravitational waves have never been directly observed. However, they are a fundamental prediction of Einstein’s theory of general relativity. Detecting them would provide an important test of our understanding of gravity. It would also provide important new insights into the physics of black holes. Large instruments capable of detecting gravitational waves from outer space have been built in recent years. Even more powerful instruments are under construction. The moment they detect their first gravitational wave, you are sure to hear about it!  

What is inside a black hole?

  We cannot glimpse what lies inside the event horizon of a black hole because light or material from there can never reach us. Even if we could send an explorer into the black hole, she could never communicate back to us.  

Current theories predict that all the matter in a black hole is piled up in a single point at the center, but we do not understand how this central singularity works. To properly understand the black hole center requires a fusion of the theory of gravity with the theory that describes the behavior of matter on the smallest scales, called quantum mechanics. This unifying theory has already been given a name, quantum gravity, but how it works is still unknown. This is one of the most important unsolved problems in physics. Studies of black holes may one day provide the key to unlock this mystery.  

Einstein’s theory of general relativity allows unusual characteristics for black holes. For example, the central singularity might form a bridge to another Universe. This is similar to a so-called wormhole (a mysterious solution of Einstein’s equations that has no event horizon). Bridges and wormholes might allow travel to other Universes or even time travel. But without observational and experimental data, this is mostly speculation. We do not know whether bridges or wormholes exist in the Universe, or could even have formed in principle. By contrast, black holes have been observed to exist and we understand how they form.  

Do black holes live forever?

  Since nothing can escape from the gravitational force of a black hole, it was long thought that black holes are impossible to destroy. But we now know that black holes actually evaporate, slowly returning their energy to the Universe. The well-known physicist and author Stephen Hawking proved this in 1974 by using the laws of quantum mechanics to study the region close to a black hole horizon.  

The quantum theory describes the behavior of matter on the smallest scales. It predicts that tiny particles and light are continuously created and destroyed on sub-atomic scales. Some of the light thus created actually has a very small chance of escaping before it is destroyed. To an outsider, it is as though the event horizon glows. The energy carried away by the glow decreases the black hole’s mass until it is completely gone.  

This surprising new insight showed that there is still much to learn about black holes. However, Hawking’s glow is completely irrelevant for any of the black holes known to exist in the Universe. For them, the temperature of the glow is almost zero and the energy loss is negligible. The time needed for the black holes to lose much of their mass is unimaginably long. However, if much smaller black holes ever existed in the Universe, then Hawking’s findings would have been catastrophic. A black hole as massive as a cruise ship would disappear in a bright flash in less than a second.  

What instruments do astronomers use to find black holes?

  When our eyes look at the heavens we see the visible light from stars and other objects in the Universe. Thousands of years ago astronomers in Greece and other ancient cultures already built a detailed understanding of the night sky. Many names and concepts then developed are still in use today. However, our human eyes are actually not very sensitive and modern astronomers use sophisticated telescopes to study the Universe.  

The telescopes used by astronomers do not just study visible light. While visible light is the type of ‘electromagnetic radiation’ that our eyes can see, there are many other types of such radiation. Different types of radiation are characterized by different wavelengths. If the wavelength is much shorter than that of visible light we speak about X-rays. We encounter X-rays often in our daily lives, for example at the hospital or during security screening. If the wavelength is much larger than that of visible light we speak about radio waves. We encounter radio waves often in our daily lives, for example in radios and cell phones.  

The black holes in the Universe do not emit any detectable type of light. However, astronomers can still find them and learn a lot about them. They do this by measuring the visible light, X-rays and radio waves emitted by material in the immediate environment of a black hole. For example, when a normal star orbits around a black hole we can measure the speed of the star by studying the visible light that it emits. Knowledge of this speed can be combined with the laws of gravity to prove that the star is in fact orbiting a black hole, instead of something else. It also yields the mass of the black hole. Alternatively, when gas orbits around a black hole it tends to get very hot because of friction. It then starts emitting X-rays and radio waves. So black holes can also often be found and studied by looking for bright sources of X-rays and radio waves in the sky.  

There are many other types of electromagnetic radiation as well. Radiation that has even smaller wavelengths (and even higher energies) than X-rays is called gamma-rays. Radiation with wavelengths between those of X-rays and visible light is called ultraviolet light. We encounter ultraviolet light in our daily lives for example in fluorescent lamps. Ultraviolet telescopes allow astronomers to study things such as the composition of the gas that exists between stars. Electromagnetic radiation with wavelengths between those of radio waves and visible light is called infrared light. We encounter infrared light in our daily lives for example in heat lamps and night-vision cameras. Infrared telescopes allow astronomers to study things such the formation of stars.  

How are black holes born?

  A black hole is born when an object becomes unable to withstand the compressing force of its own gravity. Many objects (including our Earth and Sun) will never become black holes. Their gravity is not sufficient to overpower the atomic and nuclear forces of their interiors, which resist compression. But in more massive objects, gravity ultimately wins.  

Stellar-mass black holes are born with a bang. They form when a very massive star (at least 25 times heavier than our Sun) runs out of nuclear fuel. The star then explodes as a supernova. What remains is a black hole, usually only a few times heavier than our Sun since the explosion has blown much of the stellar material away.  

We know less about the birth of supermassive black holes, which are much heavier than stellar-mass black holes and live in the centers of galaxies. One possibility is that supernova explosions of massive stars in the early Universe formed stellar-mass black holes that, over billions of years, grew supermassive. A single stellar-mass black hole can grow rapidly by consuming nearby stars and gas, often in plentiful supply near the galaxy center. The black hole may also grow through mergers with other black holes that drift to the galactic center during collisions with other galaxies. Astronomers are actively investigating these and other scenarios through observations and computer simulations.  

How do black holes grow?

  Black holes grow in mass by capturing nearby material. Anything that enters the event horizon cannot escape the black hole’s gravity. So objects that do not keep a safe distance get swallowed.  

Despite their reputation, black holes will not actually suck in objects from large distances. A black hole can only capture objects that come very close to it. They’re more like Venus’ Flytraps than cosmic vacuum cleaners. For example, imagine replacing the Sun by a black hole of the same mass. Permanent darkness would fall on Earth, but the planets would continue to revolve around the black hole at the same distance and speed as they do now. None of the planets would be sucked into the black hole. Our Earth would be in danger only if it came within some 10 miles of the black hole, much less than the actual distance of Earth from the Sun (a comforting 93 million miles).  

The diet of known black holes consists mostly of gas and dust, which fill the otherwise empty space throughout the Universe. Black holes can also consume material torn from nearby stars. In fact, the most massive black holes can swallow stars whole. Black holes can also grow by colliding and merging with other black holes. This growth process is what can reveal the presence of a black hole. As gas falls toward a black hole, it is heated to high temperatures, generating powerful radio waves and X-rays that can be studied by astronomers.  

How many black holes are there?

  There are so many black holes in the Universe that it is impossible to count them. It’s like asking how many grains of sand are on the beach. Fortunately, the Universe is enormous and none of its known black holes are close enough to pose any danger to Earth.  

Stellar-mass black holes form from the most massive stars when their lives end in supernova explosions. The Milky Way galaxy contains some 100 billion stars. Roughly one out of every thousand stars that form is massive enough to become a black hole. Therefore, our galaxy must harbor some 100 million stellar-mass black holes. Most of these are invisible to us, and only about a dozen have been identified. The nearest one is some 1,600 lightyears from Earth. In the region of the Universe visible from Earth, there are perhaps 100 billion galaxies. Each one has about 100 million stellar-mass black holes. And somewhere out there, a new stellar-mass black hole is born in a supernova every second.  

Supermassive black holes are a million to a billion times more massive than our Sun and are found in the centers of galaxies. Most galaxies, and maybe all of them, harbor such a black hole. So in our region of the Universe, there are some 100 billion supermassive black holes. The nearest one resides in the center of our Milky Way galaxy, 28 thousand lightyears away. The most distant we know of lives in a quasar galaxy billions of lightyears away.  

The Known Universe

Tools ‹ Phenomena in Universe — WordPress

Tools ‹ Phenomena in Universum — WordPress.

Between the Absolute and the Universal

Making a terminological step away, we always risk being misunderstood; in any case one can’t reach an agreement with everyone. Therefore, using the existing sense of notions, we have to try expressing something, that can’t be expressed in any concrete form initially by simplifying the searched meaning boiling it down to concrete notions. The Absolute is something comprehensive and self sufficient due to its ultimate common nature; where every part, everything that can be named, outlined, compared or related to something can’t be called the Absolute. Everything that exists within the Absolute belongs to it and can’t be related to it. The Universum has also a self-sufficient common essence, but its self-sufficiency is provided by the correlation, mutually complemented by the correlation of its parts. To put it differently, the Universum is a homeostatic integrity that possesses the quality, which can be compared to the qualities of its content and obviously this integrity aspires to the retaining of its content originality. From these definitions we can conclude that any Universum will always be a part of the only Absolute. So all our Universe, space and time continuum (not necessarily of a material nature) with the composition of physical laws, which allow a slight subtle disharmony, and saves us from the entropic desert and processes of the progressive development – this integrity has some general quality and to the full extent can be called the Universum. Apart from the purely physical reality with conformity to natural laws, describing its changes, this Integrity has first of all qualities and characters of the higher hierarchy (order). There is nothing mystic, the beyond (in the direct sense of this meaning) within this higher entity and the professional physicist, especially a synergetic expert, will agree that such global unity should have a range of the integrity’s qualities, which are not natural for its elements. But unfortunately synergetics appeared only a few decades ago, the phenomenon existed all through the time (at least according to human standards) and the human comprehended and perceived it one way or the other. Not always and not all people had a perception which is formed by the social way in today’s civilization. In other times when knowledge wasn’t systemized in contemporary scientific forms people used to personify these essences of the Universum, although according to their complexity and importance in the Universum these (“objects”? “subjects”?) these phenomena surpass the essence of the “persona” of the separately taken human personality comparatively in the same way as the latter one – the persona, say of the house mouse, the persona of a birch tree or of a piece of granite – to whatever extent it makes sense to use this notion in this example. The Universum is self sufficient and all that happens in it depends on its comprehensive quality and the internal organization, the Hierarchy of the Phenomena works for the purpose of retaining the homeostasis of the Integral. The struggle of internal forces and a range of contradictory tendencies help renewing internal “elements”, which combine qualities of physical as well as a globally essential (spiritual) nature according to the tasks of the internal development. The development fits in the Cycles according to the Laws of the Universum in general direction, the Path. In the Absolute a single whole quality of the Universum is its one Face, Name of the Sense. Are there any other forms of the Universum within the Absolute – or is it that its content can’t be repeated in its diversity? This question is at least incorrect, for the Absolute has everything which can or can’t be, something that nobody will ever be able to imagine – otherwise it wouldn’t be Absolute. For us, being inside the Universum, inside the determination of the Sense, such question can’t have a meaning, while we are interacting only with qualities and essences – parts, representing It. The Endless Universe is closed in; the time notions of the beginning and the end of the World only give us inkling on the existence of the “shell” in the higher dimensions. But the Integrity itself can interrelate with something greater in the space of the Absolute with endless numbers of dimensions, since absolutely everything is possible within the Absolute. Such special interactions should have appropriate meanings even in their slightest manifestations; and to some extent they are rather invigorating for the Integrity – for the external interference, which doesn’t involve destructive force, always boosts processes of development, and adds up the energy for the internal dynamics of a homeostatic system. And we probably are not to be given a chance to see the existing beyond the Universum, its problems are our problems. The human spends the energy of the soul, gives it to the Universum, and forms a quality within him, gaining the information of a higher order, fulfilling within himself the tasks of the Universal movement – the Will of God. Opposite tendencies verify and strengthen these aspirations, making selection by temptations and seductions, the depersonalized essence of which could be compared to the processes of dissimilation for the Higher Nature. And if a certain person disregards the necessity to live according to the laws of the Unity, if his personal tasks prevail over spiritual values, he makes his choice in favor of dissimilative structures, falling in to the track of the appropriate processes with all out coming subsequences. As you may see this scientific version of description provides us with flat model like but rather concrete perspectives. And I humbly seek your apologies for intruding by these methods in the sphere, which can’t be fathomed by Earthly standards.