An American researcher claims, based on a method developed in Israel, that a large part of the planets discovered outside the solar system are not planets at all. Not everyone agrees with him
By: Avishai Gal-Yam
A planet in the illustration is not visible from Earth. We learn about its existence in an indirect way: its gravity causes the oscillation of the star around which it circled. As the star moves away from us, the light emitted from it tends to red; As it approaches, the light tends to blue
It is customary to define planets like the Earth as relatively small bodies that revolve around a star, the sun for example. The planets do not emit their own light: the reason we see them is that they reflect the sunlight that hits them. The sun, on the other hand, emits an enormous amount of light and energy, as a result of nuclear processes constantly occurring in its center. Except for the nine planets in our solar system, all the stars that appear in the night sky are stars like the sun, which are at a great distance from us and therefore appear to us much smaller and pale compared to the sun. To avoid confusion between stars like the sun and planets, some call the planets "planets" in Hebrew as well.
Apparently, the difference between stars and planets is clear: stars are very large and emit a lot of light, while planets are much smaller and do not emit light but reflect the light of the star around which they orbit. However, in recent years it has become clear that the distinction between stars and planets is not so sharp.
Astronomers have known for many years that there is a great difference in the size of different stars. The Sun is an average-sized star, but there are stars much larger than the Sun and others many times smaller. Researchers studying the structure of stars calculated and showed that nuclear processes cannot exist in the center of very small stars. There is a minimum mass, about eight percent of the mass of our Sun, below which the stars will not have a nuclear energy source and therefore they will emit almost no light. The nickname "brown dwarfs" was attached to these small and dark stars. Indeed, several such brown dwarfs have been detected in observations from recent years.
The sun is a single star: there are no other stars in its immediate vicinity. However, most of the stars are not like that: it turns out that they are arranged in pairs, or larger groups, of stars moving around each other. It is quite possible that one of them will be much bigger than its friend. In fact, it is possible for a Sun-like star to have a companion that is a brown dwarf. This is precisely where the difficulty lies: is there a real difference between a pair of stars, one of which is a brown dwarf, and a star that has a very large planet?
Well, it is common to assume that such a difference does exist. An accepted definition of the difference between planets and brown dwarfs lies in their different creation processes. It is commonly assumed that stars are formed from clouds of gas, mainly hydrogen, found in space. These clouds collapse and shrink under the influence of gravity, until they become stars of various sizes. Sometimes, a single star, such as the Sun, is formed from such a gas cloud. However, many times the cloud is divided during the collapse into several parts and a separate star is formed from each of them. A pair of stars, one of which is a brown dwarf, formed from the same original cloud, except that one part was much larger than the other.
After the star is formed from the gas cloud, a disk of "residue" is formed around it: mainly small particles of interstellar dust and gas, in which a relatively high concentration of elements heavier than hydrogen, such as carbon, oxygen, nitrogen and iron. From this disk the planets are formed. The composition of the disk explains the composition of the planets which is different from that of the star formed directly from the hydrogen gas clouds. According to this distinction, a brown dwarf forms directly from an interstellar gas cloud while a planet forms from a disk around a star.
This difference between a planet and a brown dwarf explains the great importance that scientists attach to determining whether a certain discovered object is a planet or a brown dwarf. The discovery of a planet around a distant star similar to the Sun proves that around this star there once existed a disk from which planets formed. It is possible, therefore, that other planets other than the one that was discovered formed around this planet, which may be similar to the Earth and therefore allow the existence of life. If, on the other hand, it turns out that the discovered object is a brown dwarf, then it is in fact a pair of stars, one of which is particularly small: this has nothing to say about the possibility of the existence of Earth-like planets or the existence of life in this system. The controversy in the community of astronomers, some of whom have reported in recent years on the discovery of objects - most likely planets - orbiting sun-like stars, focuses on exactly this point.
Since planets do not emit their own light, but reflect the light of the stars around which they orbit, the amount of light coming from a planet orbiting a distant star is extremely small; So small that the planet cannot be observed directly, even with the best telescopes. That is why the researchers' reports regarding planets outside our solar system are based on indirect evidence of their existence. The main method of detecting planets outside the solar system is based on their influence on the stars around which they orbit. As we know, gravity causes an attraction between any two bodies. The effect of the Sun's gravity on the planets causes them to circle in elliptical orbits around it. Similarly, the gravitational influence of the planets causes the movement of the sun, but this oscillation is very small because the mass of the sun is much greater than that of the planets. If a star similar to the Sun, but many light years away from us, has a large enough planet, moving in an orbit close to it, it may cause it to have a relatively large oscillation, which we can measure.
Measuring such fluctuations of stars is based on a physical effect known as
"Doppler effect". The oscillation of a star due to some object (such as a planet) the holiday
around it, causing it to move cyclically: once in our direction and once away
from us The Doppler effect makes the star's light appear redder
When it moves away from us and bluer when it comes closer to us. measuring instruments
New and extremely accurate are able to measure the smallest changes
in the distribution of the star's light and discover the cyclical change (to red
and to blue) which indicates the star's oscillation as a result of the effect of gravity
The holiday bone around him. In this way it is possible to discover the existence of an infinite object
It will be seen orbiting the star, and distinguish the planets if they are relatively heavy.
The Doppler effect measurement method has one major limitation. She
It does not allow to determine exactly the mass of the invisible bone that causes the oscillation
which they discover, but only to determine that this mass is greater than a minimum mass
a certain This is because the magnitude of the measured oscillation of the star depends not only
in the mass of the invisible object but also in the angle between the orbit in which the object orbits the
the star and the line of sight between the star and us. A relatively heavy bone (eg
a brown dwarf) moving at a large angle to the line of sight or a relatively light object (eg
planet) moving at a small angle to the line of sight will result in measuring a fluctuation in intensity
Similar. The researchers usually estimate what is the most reasonable mass for each body
which is discovered (usually, based on the assumption that it is likely that the angle is not very
large) and accordingly, is it likely that this is a new planet, but usually
It is not possible to determine the mass unequivocally.
Prof. Zvi Maza from Tel Aviv University and his student Shai Zucker developed
An innovative method, which allows solving this problem in some cases. The method
is based on a combination of Doppler measurements and accurate observations
From the "Hypercos" satellite. This satellite measured with great precision the position of
stars in the sky and is able to notice the slightest fluctuation of a star around
His permanent position in the sky. This is in contrast to the Doppler measurement, which can determine
Only if the star is moving away or approaching us. The satellite data makes it possible
Distinguish between the two cases we mentioned earlier: a star that has a heavy partner
moving at a large angle around it will move noticeably in the sky and this movement
will be measured by "Hyperkos". Conversely, a star that has a moving light partner
At a small angle it will hardly change its position in the sky and will therefore appear as a star
Constant in the measurements of "Hyperkos".
With the help of this innovative method, Maza and Zucker proved that some systems in question
Eliahan initially believed that the discovered partner was, most likely, a planet
relatively heavy, actually contained partners with a much greater mass, that is,
stars or brown dwarfs.
Following the work of the two, the American astronomer David
Black uses a similar method to test all systems where a discovery has been reported
planets. Based on his research, Black recently published a claim according to which some
The largest, and perhaps most, of these systems contain no planets at all
And most importantly. In most cases, according to him, these are pairs of stars, one of which is
extremely small. This claim almost immediately became the subject of a heated dispute between
The researchers involved in the field. If it is true, then a considerable part of the justification
for the intensive occupation and the investment of a lot of resources in this field, i.e., examination
The possibility of life throughout the universe is out of place, since the discovery of couples
Stars do not indicate the possibility of the existence of spherical planets
Country.
Prof. Maza believes that Black's claim is true in some cases and that in a small part
Of the planets whose discovery was reported, they are indeed not planets at all. However, his claim
Black's sweeping conclusion that there are no planets around most of the stars examined,
is not justified in Maza's opinion. Moreover: other works of Maza,
Together with his students Shai Zucker and Dorit Goldberg and other researchers
from abroad, shows that the characteristics of the objects discovered and reported as "planets"
are fundamentally different from those of minor partners in pairs of stars.
The controversy, in any case, has not yet died down, and it rages over the pages of
The scientific newspapers in the field.
{Appeared in Haaretz newspaper, 6/12/2000{
One response
oh …………..
I didn't know it looked like this, it's very interesting, come in