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December 19, launched from the Kourou Cosmodrome in French Guiana Russian rocket Soyuz. On board the rocket was a space Gaia Observatory (Global Astrometric Interferometer for Astrophysics, i.e. global astrometric astrophysical interferometer). Located at the second point of Lagrange, the apparatus will collect data on the Milky Way, dark matter and exoplanets. The cost of the mission is about a billion dollars, and because colossal size of the CCD of the telescope (it contains more than a billion pixels), the device received the nickname “The largest digital camera in the world. “Gaia was supposed to fly into space a month earlier, November 19, 2013. At the end of October, however, suspicion arose, that transponders (signal transmitters) on board the device may be defective. In the message of the European the space agency said that the reason for suspicion was incorrect operation of the same transponders in another (unnamed) space mission. Agency engineers decided not to risk it and replace parts. For this, the telescope had to be returned to Europe, and launch has been delayed.
Gaia and the stars
The main purpose of the device is to collect data on the stars that make up Milky Way. In total, it is planned to analyze data on a billion stars, building on the basis of the collected statistics the most accurate on Today is a map of our galaxy. But how exactly is planned to solve such a large-scale problem?
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Scientists collect CCDs for Gaia Photo: ESA
Gaia – a high-precision observatory, on board which are installed two telescopes. Light collected by telescopes hits a block of 106 individual highly sensitive CCD matrices. Together they form an array whose linear dimensions are 100 by 50 centimeters, and the resulting resolution can reach a billion pixels. it The main working tool of the observatory. In addition to telescopes on the board has a photometer and spectrometer.
“To determine the coordinates of stars in three-dimensional space “Gaia” uses the astronomical parallax method, – said Lente.ru, professor at the University of Missouri, Sergey Kopeikin. – The position of the star visible in the sky changes as it moves. spacecraft in orbit. Magnitude of this change is straight proportional to the distance to the star. By measuring the amount of displacement stars in the sky for one year, you can pinpoint distance to a star, expressed in astronomical units (average distance from Earth to the Sun). ”
50 gigabytes per day
The scope of each of the telescopes of the observatory relatively small. To cover the heavenly sphere, Gaia will rotate around its own axis. With this movement, the light from each of the stars will pass through a CCD matrix divided into several functional sectors. It is planned that when passing through the first and the second columns of the matrix (column by telescope) computer selects the stars to be monitored.
Then the light will fall on the main (astrometric) part of the matrix. It is tuned so that light from the star is detected only a relatively small number of pixels, a kind of frame around the star. This is done so that information can be have time to process. It is the data obtained here that are supposed use for astronomical parallax method. The astrometric part is common to both telescopes.
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Gaia Image: ESA
After the main part of the matrix, the light of the star will fall on the columns matrices that are responsible for measuring the photometer. Going here spectrum information that allows temperature and chemical composition of the star. Finally, the last sector of the matrix Designed for spectrometric analysis. Data from here to Based on the Doppler effect, radial velocity can be determined. stars (that is, the projection of its speed on a straight line connecting observer and the star itself). Information Collected – About 50 gigabytes per day – transmitted to Earth. In just 6 years of operation, Gaia should transfer to scientists more than a petabyte of data.
The main thing, however, is not quantity, but the quality of information. “Modern technology on board the device allows you to get very high accuracy of measurement. “Gaia” allows you to measure the angle in the sky between two-star directions, with an accuracy of 25 microseconds of arc. This corresponds to the angle under which, for example, a coin is visible. worth 25 US cents on the surface of the moon. Most accurate astrometric measurements carried out before Gaia were achieved using ultra-long base radio interferometry, where an accuracy of 10 microseconds of arc was achieved. However these measurements are taken only for individual objects in the sky, while while Gaia will measure the parallax of millions of stars, “- said Sergey Kopeikin.
Dark matter and stuff
Why might scientists need so much data? IN first of all, information about the position of stars and their speeds will allow significantly clarify the size and structure of our galaxy. More In addition, it will allow you to more accurately estimate the amount of dark in the Milky Way matter (or hidden mass) – a mysterious substance that involved in the gravitational, but not involved in the electromagnetic interaction. It is known that this matter is many times more than visible matter – it is also called baryonic. To evaluate this number of scientists need to know the dependence of the speed of stars on their the distance from the center of the Milky Way (at one time the analysis of such patterns led to the discovery of the darkest matter).
Gaia is part of the European science program a space agency called Horizon 2000 Plus. Within This program launched the Herschel telescope. He was at the point L2, but, unlike the Gaia, was located so that always stay in the earthly partial shade (there is no complete shadow at the libration point, so how sunlight scattered by the atmosphere gets there). In June 2013 telescope officially completed the mission and was put on orbit around the sun.
“Information on the movement of stars is useful in high-precision experiments to test general relativity (GR) with double pulsars. Gaia will itself allow for an independent verification of general relativity by observing the effect of deflection of light rays, coming from the stars, by the gravitational field of the sun. Given the fact that Gaia will measure the positions of stars with an accuracy of 25 microseconds arcs and will collect huge statistical material, accuracy checks GTR in the solar system will surpass previous experiments on at least one gravitational deflection of light by the Sun order, “Professor Kopeikin told Lente.ru.
Also, the device is planned to be used to search for exoplanets. The fact is that each of the stars in the future Gaia catalog will be observed at least 70 times. Theoretically, this will allow analyze the light curves of stars and their spectra to detect they have anomalies that may indicate the presence in the system the planet. Finally, according to the creators, the space observatory can be adapted to observe asteroids.
Second Lagrangian point
To complete all the tasks required, the equipment the telescope always remained at maximum sensitivity – because, as they said, she will have to observe more than a billion stars. That is why the device was decided to be placed in neighborhood of the so-called second Lagrangian point (L2, or points libration) of the Earth-Sun system.
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Lagrange points in the Earth-Sun system
Libration points arise in one of the simplified versions of the problem. three bodies In this simplification, it is assumed that the mass of two bodies much larger than the third, so it (the third) in the first two does not affects. As a result, it turns out that such a system exists points where the attractive forces of two massive bodies are balanced centrifugal forces. There are only five such points. Three of them located on a straight line connecting the centers of mass of the first two bodies. IN the Earth-Sun system, the second point is approximately 1.5 million kilometers from the Earth.
The second Lagrange point is a point of unstable equilibrium – this means that the slightest disturbance of the apparatus leads to the fact that he eventually leaves the neighborhood of the point. To hold apparatus in the vicinity of L2, you will need fuel. Stock on board the device will last for several years.
Around the Lagrange point “Gaia” will move along the so-called Lissajous curves – analogues of orbits in the vicinity of the libration point. Thanks to this, in particular, the Earth will not block the sun light and the apparatus will be able to receive enough energy with the help of its solar panels. The main advantage of the second libration point is the stability of the environment of the device – for example, it is not will have to switch from day to night. This kind transitions always negatively affect sensitivity equipment.
Gaia will begin to transmit the first data very soon. Scientists all over the world are waiting for them to show “the world’s largest digital camera. “When asked if the information from Gaia would be useful to him, Professor Sergey Kopeikin replies: “Of course, I will use the results of Gaia for a better understanding of nature gravitational field in the general theory of relativity. Or maybe in possible generalizations in the field of quantum field theory. ”
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