Category: universe

Kepler-16b is an extrasolar planet. It is a …

Kepler-16b is an extrasolar planet. It is a Saturn-mass planet consisting of half gas and half rock and ice, and it orbits a binary star, Kepler-16, with a period of 229 days. “It Is the first confirmed, unambiguous example of a circumbinary planet – a planet orbiting not one, but two stars,“ said Josh Carter of the Harvard-Smithsonian Center for Astrophysics, one of the discovery team.

Kepler-16b was discovered using the space observatory aboard NASA’s Kepler spacecraft. Scientists were able to detect Kepler-16b using the transit method, when they noticed the dimming of one of the system’s stars even when the other was not eclipsing it.

source | video

Do you think that once Smith's Cloud coll…

Do you think that once Smith's Cloud collides with the Milky Way, it will survive the collision to resuscitate the formation of stars in our dying (or possibly dead) Galaxy?

Very interesting it.

Although, really, I do not know for sure, but possibly its collision can generate a new explosion of star formation, although it may take millions of years for this to happen.

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Smith’s cloud is a cloud of hydrogen and high speed, it is expected that it will collide with the Perseus arm of our galaxy. The impact will compress gas clouds on that spiral arm, causing a brilliant burst of star formation.

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But it offers no danger, for, however large (10 000 or 11 000light-years), it is very small compared to the Milky Way.

Trajectory of Smith Cloud

Here is an article about this:

https://science.nasa.gov/news-articles/massive-cloud-collision-course-milky-way

This colorful image, taken by the Hubble Space…

This colorful image, taken by the Hubble Space Telescope, celebrates the Earth-orbiting observatory’s 28th anniversary of viewing the heavens, giving us a window seat to the universe’s extraordinary stellar tapestry of birth and destruction. At the center of this image is a monster young star 200,000 times brighter than our Sun that is blasting powerful ultraviolet radiation and hurricane-like stellar winds, carving out a fantasy landscape of ridges, cavities, and mountains of gas and dust.

Image Credit: NASA, ESA, and STScI

Hubble celebrates 28th anniversary with a trip…

Hubble celebrates 28th anniversary with a trip through the Lagoon Nebula

Approaching the Universe’s origins

Approaching the Universe’s origins

What is an Exoplanet?

An exoplanet or extrasolar planet is a planet outside our solar system that orbits a star. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such. However, the first scientific detection of an exoplanet was in 1988. Shortly afterwards, the first confirmed detection was in 1992. As of 1 April 2018, there are 3,758 confirmed planets in 2,808 systems, with 627 systems having more than one planet.

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The High Accuracy Radial Velocity Planet Searcher (HARPS, since 2004) has discovered about a hundred exoplanets while the Kepler space telescope (since 2009) has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives.

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In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars have an “Earth-sized” planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, one can hypothesize that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.

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The least massive planet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead.

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There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit.

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Some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way. Nonetheless, evidence suggests that extragalactic planets, exoplanets further away in galaxies beyond the local Milky Way galaxy, may exist. The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun.

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Besides exoplanets, there are also rogue planets, which do not orbit any star and which tend to be considered separately, especially if they are gas giants, in which case they are often counted, like WISE 0855−0714, as sub-brown dwarfs. The rogue planets in the Milky Way possibly number in the billions (or more).

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Some planets orbit one member of a binary star system, and several circumbinary planets have been discovered which orbit around both members of binary star. A few planets in triple star systems are known and one in the quadruple system Kepler-64.

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Methods of detecting exoplanets

1° Radial velocity

A star with a planet will move in its own small orbit in response to the planet’s gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star’s spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet using the binary mass function.

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2º Transit photometry

While the radial velocity method provides information about a planet’s mass, the photometric method can determine the planet’s radius. If a planet crosses (transits) in front of its parent star’s disk, then the observed visual brightness of the star drops by a small amount; depending on the relative sizes of the star and the planet. 

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3° Direct Imaging

Exoplanets are far away, and they are millions of times dimmer than the stars they orbit. So, unsurprisingly, taking pictures of them the same way you’d take pictures of, say Jupiter or Venus, is exceedingly hard.

New techniques and rapidly-advancing technology are making it happen.

The major problem astronomers face in trying to directly image exoplanets is that the stars they orbit are millions of times brighter than their planets. Any light reflected off of the planet or heat radiation from the planet itself is drowned out by the massive amounts of radiation coming from its host star. It’s like trying to find a flea in a lightbulb, or a firefly flitting around a spotlight.

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On a bright day, you might use a pair of sunglasses, or a car’s sun visor, or maybe just your hand to block the glare of the sun so that you can see other things.

This is the same principle behind the instruments designed to directly image exoplanets. They use various techniques to block out the light of stars that might have planets orbiting them. Once the glare of the star is reduced, they can get a better look at objects around the star that might be exoplanets.

4° Gravitational Microlensing

Gravitational microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than a thousand such events have been observed over the past ten years.

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If the foreground lensing star has a planet, then that planet’s own gravitational field can make a detectable contribution to the lensing effect. Since that requires a highly improbable alignment, a very large number of distant stars must be continuously monitored in order to detect planetary microlensing contributions at a reasonable rate. This method is most fruitful for planets between Earth and the center of the galaxy, as the galactic center provides a large number of background stars.

5° Astrometry

This method consists of precisely measuring a star’s position in the sky, and observing how that position changes over time. Originally, this was done visually, with hand-written records. By the end of the 19th century, this method used photographic plates, greatly improving the accuracy of the measurements as well as creating a data archive. If a star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. 

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Effectively, star and planet each orbit around their mutual centre of mass (barycenter), as explained by solutions to the two-body problem. Since the star is much more massive, its orbit will be much smaller. Frequently, the mutual centre of mass will lie within the radius of the larger body. Consequently, it is easier to find planets around low-mass stars, especially brown dwarfs.

Spiral Galaxy NGC 2841 Image Credit: Hubbl…

Spiral Galaxy NGC 2841

Image Credit: Hubble, Subaru; Composition & Copyright: Roberto Colombari

Lagoon Nebula registered by Robert M P Siqueir…

Lagoon Nebula registered by Robert M P Siqueira – Brazil

Alnitak Region with the Horse Head and Flame…

Alnitak Region with the Horse Head and Flame Nebulae

by

Warren Keller

An interesting galaxy has been circled in th…

An interesting galaxy has been circled in this NASA/ESA Hubble Space Telescope image. The galaxy — one of a group of galaxies called Luminous Red Galaxies — has an unusually large mass, containing about ten times the mass of the Milky Way. However, it’s actually the blue horseshoe shape that circumscribes the red galaxy that is the real prize in this image.

This blue horseshoe is a distant galaxy that has been magnified and warped into a nearly complete ring by the strong gravitational pull of the massive foreground Luminous Red Galaxy. To see such a so-called Einstein Ring required the fortunate alignment of the foreground and background galaxies, making this object’s nickname “the Cosmic Horseshoe” particularly apt.

The Cosmic Horseshoe is one of the best examples of an Einstein Ring. It also gives us a tantalising view of the early Universe: the blue galaxy’s redshift — a measure of how the wavelength of its light has been stretched by the expansion of the cosmos — is approximately 2.4. This means we see it as it was about 3 billion years after the Big Bang. The Universe is now 13.7 billion years old.

Credit:ESA/Hubble & NASA