When we imagine distant stars, we usually think of distances of tens, hundreds, or thousands of light years. All these luminaries belong to our Galaxy - the Milky Way. Modern telescopes are able to resolve stars in the nearest galaxies - the distance to them can reach tens of millions of light years. But how far do the possibilities of observational technology extend, especially when nature helps it? The recent astonishing discovery of Icarus - the most distant star in the universe known to date - indicates the possibility of observing extremely distant cosmic phenomena.
Help of nature
There is a phenomenon due to which astronomers can observe the most distant objects of the Universe. It is called one of the consequences general theory relativity and is associated with the deflection of a light beam in a gravitational field.
The lensing effect lies in the fact that if any massive object is located between the observer and the light source on the line of sight, then, by bending in its gravitational field, a distorted or multiple image of the source is created. Strictly speaking, the rays are deflected in the gravitational field of any body, but most noticeable effect give, of course, the most massive formations in the Universe - clusters of galaxies.
In cases where a small cosmic body, such as a single star, acts as a lens, the visual distortion of the source is almost impossible to fix, but its brightness can increase significantly. This event is called microlensing. Both types of gravitational lensing have played a role in the history of the discovery of the most distant star from Earth.
How did the discovery happen
The discovery of Icarus was facilitated by a happy accident. Astronomers have been observing one of the distant MACS J1149.5+2223, located approximately five billion light-years away. It is interesting as a gravitational lens, due to the special configuration of which light rays are bent in different ways and eventually travel different distances to the observer. Consequently individual elements lensed image of the light source must be delayed.
In 2015, astronomers were waiting for the Refsdal supernova predicted by this effect in a very distant galaxy, the light from which reaches the Earth in 9.34 billion years. The expected event actually happened. But in the 2016-2017 images taken by the Hubble telescope, in addition to the supernova, something else was found that was no less interesting, namely the image of a star belonging to the same distant galaxy. By the nature of the brilliance, it was determined that this is not a supernova, not a gamma-ray burst, but an ordinary star.
It became possible to see a single star at such a huge distance thanks to a microlensing event in the galaxy itself. Randomly, an object passed in front of the star - most likely another star - with a mass of the order of the sun. He himself, of course, remained invisible, but his gravitational field increased the brilliance of the light source. In combination with the lensing effect of the MACS J1149.5+2223 cluster, this phenomenon resulted in an increase in the brightness of the most distant visible star 2000 times!
A star named Icarus
The newly discovered luminary was given the official name MACS J1149.5+2223 LS1 (Lensed Star 1) and given name- Icarus. The previous record holder, who held the proud title of the most distant star that could be observed, is located a hundred times closer.
Icarus is extremely bright and hot. This is a blue supergiant of spectral class B. Astronomers have been able to determine the main characteristics of the star, such as:
- mass - not less than 33 solar masses;
- luminosity - exceeds the solar approximately 850,000 times;
- temperature - from 11 to 14 thousand kelvin;
- metallicity (content chemical elements heavier than helium) - about 0.006 solar.
The fate of the most distant star
The microlensing event that made it possible to see Icarus occurred, as we already know, 9.34 billion years ago. The universe was then only about 4.4 billion years old. A snapshot of this star is a kind of small-scale freeze-frame of that distant era.
In the time that light emitted more than 9 billion years ago traveled the distance to Earth, the cosmological expansion of the universe pushed the galaxy in which the most distant star lived to a distance of 14.4 billion light years.
Icarus himself, according to modern ideas about the evolution of stars, ceased to exist long ago, because the more massive the star, the shorter should be its lifetime. It is possible that part of the substance of Icarus served building material for new luminaries and, quite possibly, their planets.
Will we see him again
Despite the fact that a random act of microlensing is a very short-term event, scientists have a chance to see Icarus again, and even with greater brightness, since in the large lensing cluster MACS J1149.5+2223 many stars should be near the line of sight of Icarus - Earth, and cross this beam can be any of them. Of course, it is possible to see other distant stars in the same way.
Or maybe someday astronomers will be lucky to record a grandiose explosion - a supernova explosion, with which the most distant star ended its life.
When you look at the sky on a dark night in clear weather, you see many stars. However, almost all of them are in our galaxy, milky way. Even the most distant ones that you can see without a telescope are less than twenty thousand light-years from Earth. It may seem like a gigantic distance, but the cosmos is much larger than our immediate surroundings. It is really huge, which is why it is incredibly difficult for scientists to study stars outside our galaxy. The most distant star that has been isolated from the extraneous glow surrounding it is only 55 million light-years away from us.
Scientific achievements
However, if astronomers are not mistaken in anything, this record was recently broken. According to an article published in March this year in the journal Nature Astronomy, he was smashed to smithereens, swept away and trampled. He moved on to a star that is 14 billion light years away from us! It should be noted that astronomers often manage to see objects far from our planet. With telescopes, they can see the brightest supernovae 10 billion light years away. However, ordinary stars cannot be seen even at a distance hundreds of times smaller. And here we first mention about "gravitational lensing".
This phenomenon occurs when the enormous mass of a galaxy, or even a cluster of galaxies, bends, distorts, and amplifies the light behind it. This phenomenon is possible due to the fact that such objects actually bend the very space around them. Galaxies that create the effect of gravitational lensing "amplify" the brightness by an average of 50 times.
distant stars
The star we're talking about today is behind a cluster of galaxies 6 billion light-years away, and its light has been amplified by more than 2,000 times! In scientific catalogs, it is listed as MACS J1149 Lensed Star 1. However, the scientists who discovered it also gave it an unofficial name - Icarus. Thank you very much for this, it is much more convenient for us as well.
Icarus was spotted, quite by accident, when researchers looked at supernova images taken by the Hubble Space Telescope in 2016 and 2017. Not far from her, they noticed a small bright spot. It changed brightness over time, but not in the same way that supernovae do. The color scheme of the light coming from this object remained unchanged for many months. Further analysis showed that we are dealing with a blue supergiant.
These stars are much larger, more massive, hotter than the Sun and hundreds of thousands of times brighter than it. This is such a small reminder that any phenomenon in space can be truly cosmic in scale. All blue supergiants have similar characteristics, therefore, by comparing the light of Icarus with the light of the same objects in our galaxy, astronomers were able to calculate the distance to it. It turned out that the star has an age of 9 billion years, and due to the fact that the Universe is expanding, now the luminaries are generally 14 billion light years before that.
How did Icarus manage to magnify his image by 2000 times when the usual gravitational lensing value is only 50? The answer is microlenses. These are small objects inside large lenses. These can be individual stars, providing an additional approximation of the "picture". Lenses within lenses. This effect does not last long, because the microlenses are constantly moving from the desired position and returning to it again. However, if we carefully follow what is happening, huge opportunities open up before us. With the help of microlensing, scientists have even managed to find planets outside the Milky Way!
the most distant star
Icarus, by the way, can be useful not only as a record holder, listed in the relevant book. By studying how the approach effect affects it over time, astronomers hope to build an accurate model of the distribution of matter in a “lensing” cluster of galaxies. This probably includes dark matter, which we still can’t find, examine and feel, but which has a gravitational effect on others. space objects. In this way, Icarus can help us greatly increase our knowledge of the universe. Well, his ancient Greek namesake was also a very positive character, although he did not become a champion, no matter how hard he tried. We hope that our Icarus will not disgrace the glorious name.
The ancients believed that all the stars were on the same distance from the Earth, attached to a crystal sphere. In ancient times, the Earth was considered the fixed center of the universe, around which the sun, moon, planets and stars revolved. The nature of the celestial bodies was unknown at that time, and only a very few philosophers believed that the stars were, in fact, distant suns.
This idea began to spread only after the appearance of the teachings of Copernicus in the 16th century. To explain the irregularities in the movement of the planets across the sky, Copernicus suggested that the center of the universe is not the Earth, but the Sun, around which the planets revolve. The Earth, having lost the status of the center, became just one of the planets: now it did not rest motionless, but revolved around the Sun in an orbit. Then some scientists had the idea to measure the distances to the stars. The method they proposed is called the annual parallax method.
The idea was simple and was as follows. If you constantly measure the position of a star in the sky, you can see how the star describes tiny ellipses in space with a period of 1 year. The displacement of the star must occur due to the movement of the Earth in orbit around the Sun, and its magnitude will be the greater, the closer the star is to us. Knowing the magnitude of the displacement angle or, in other words, the parallax of a star, one can easily find the distance to it using the formula D=a/sin(p), where a is the semi-major axis of the earth's orbit, and p is the parallax value, measured in seconds of arc.
Despite the simplicity of the method, scientists have not been able to detect parallaxes in stars for a long time. Some considered this to be evidence of the fallacy of the Copernican theory, but most believed that the stars were simply too far away from us to hope to determine their parallax.
Only in the 19th century, with the advent of a new generation of telescopes that could measure very small angles, were scientists able to reliably determine the distances to some stars. Parallax was first measured by the great Russian astronomer, the first director of the Pulkovo Observatory, Vasily Yakovlevich Struve in 1837. Observing the star Vega, he found that its parallax is 0”, 125. It's a completely negligible angle. Suffice it to say that at such an angle a person will be visible to the naked eye from a distance of 3000 kilometers!
Now it was possible to calculate the distance to this star. If the distance from the Earth to the Sun (a) is taken as 1, then D = 1 / sin (0”, 125), which is equal to 1650000. This figure shows how many times Vega is farther from the Earth than the Sun. It is inconvenient to measure such colossal distances in kilometers, so astronomers use parsecs. A parsec is the distance from which the semi-major axis of the Earth's orbit, perpendicular to the line of sight, is visible at an angle of 1 ". The distance in parsecs is equal to the reciprocal of the parallax. Since Vega's parallax is only 1/8 of a second of arc, the distance to the star is 8 parsecs.
This is a very large value. Light, moving at a speed of 300,000 km/s, will overcome this distance in 26 years. This means that the Vega light we observe was emitted by the star 26 years ago!
To date, scientists know the parallaxes of more than a hundred thousand stars. The method of annual parallaxes allowed astronomers to determine the exact distances to stars within a radius of about a hundred parsecs or 320 light years from the Sun. Distances to more distant stars are determined by other, indirect methods. But they are based on the same annual parallax method.
When observing any star from two opposite points of the globe, it is almost impossible to notice differences in the directions to the star. The stars are many times farther from the Earth than the Moon, the planets, and the Sun. The Russian scientist V. Ya. Struve managed to determine the distance to the nearest star to us. This was over a hundred years ago. To do this, he had to observe it not from the ends of the earth's diameter, but from the ends of a straight line, which is 23,600 times longer. Where could he get such a straight line that cannot fit on the globe? It turns out that this line exists in nature. This is the diameter of the earth's orbit. For half a year Earth takes us to the other side of the sun. Knowing the diameter of the Earth's orbit (and it is twice the average distance to the Sun), by measuring the angles at which the star is observed, you can calculate the distance to it.
The stars closest to us - Proxima Centauri and Alpha Centauri - are 270,000 times farther from the Earth than the Sun. A beam of light from these stars has to fly to the Earth for 4.5 years.
The distances to the stars are huge and it is inconvenient to measure them in kilometers. It turns out too many kilometers. And scientists introduced a larger unit of measure: the light year. This is the distance light travels in one year.
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Stars can be from us at distances equal to tens, hundreds, thousands of light years or more.
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The definition of distance in astronomy usually depends on how far away it is. heavenly body. Some methods can only be applied to relatively close objects, such as neighboring planets. Others are for more distant ones, such as stars or even galaxies. However, these methods are generally less accurate.
How to determine the distance to an object in space
Method for determining the distance to neighboring planets
In the solar system, this is relatively simple: the motion of the planets here is calculated according to Kepler's laws, and it is possible to calculate the distance of nearby planets and asteroids using radar measurements. In this way, it is very easy to set the distance.
Inside solar system Kepler's laws apply
How is the distance to stars measured?
For stars relatively close to us, the so-called parallax can be determined. In this case, it is necessary to observe how the position of the star changes as a result of the revolution of the Earth around our luminary relative to stars that are much more distant from us. Depending on the accuracy of the measurement, a fairly accurate and direct determination of the distance is possible.
Calculating Distances from the Parallax of Stars
If this is not suitable, one can try to determine the type of star from the spectrum in order to infer the distance from the true brightness. This is already an indirect method, since certain assumptions must be made about the star.
Measuring distances from the spectrum of stars
If it is impossible to apply this method, then scientists try to get by with a "scale of distances". At the same time, they are looking for stars whose brightness is precisely known from observations in our Galaxy. Such objects are called "standard candles". They are, for example, Cepheid stars, whose brightness changes periodically. According to the theory, the rate of these changes depends on the maximum brightness of the star.
Calculating distances from Cepheids
If such Cepheids are found in another galaxy and you can observe how the brightness of a star changes, then its maximum brightness is determined, and then the distance from us. Another example of a standard candle is a certain kind of supernova explosion, which astronomers believe always has the same maximum brightness.
A standard candle could be a supernova explosion
However, even this method has its limitations. Then astronomers use the redshift in the spectra of galaxies.
Increasing the wavelength of light coming from a galaxy makes it appear redder in the spectrum, called redshift.
Based on it, the removal rate of a galaxy can be calculated, which is directly related - according to Hubble's law - to the distance to this galaxy from the Earth.
