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Why did the standard candles fade?

New observations of supernovae that emit a constant amount of light sharpen the debate surrounding the expansion of the universe

Avishai Gal-Yam, Haaretz

The Cancer Nebula, one of the most beautiful celestial objects known today, is the remains of a supernova that exploded in 1054 at a distance of 6,500 light years from Earth
The Cancer Nebula, one of the most beautiful celestial objects known today, is the remains of a supernova that exploded in 1054 at a distance of 6,500 light years from Earth

Photo: NASA

When humans looked at the night sky at the dawn of history, they saw blood in their eyes
The star systems and celestial signs for the gods. The concept that the universe is eternal,
and studded with unchanging stars, continued to dominate the dome until the beginning of the century
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Today we know that the stars are not eternal: they are "born" from gas clouds
interstellar collapsing under the influence of gravity; are developing, and in the process
Convert huge amounts of nuclear energy into radiation, like the light of
the sun; And finally, when their nuclear fuel is used up, they die. there is
Stars, like our sun, are expected to die a "quiet death" - to cool down
and slowly fade into the interstellar darkness. But other stars,
Those who are just very overweight or have a close partner, may die
A much more dramatic and glamorous death: their lives end in a violent explosion in which she is released
A huge amount of energy and a significant part of the star is torn apart and blown away
everywhere. Such an explosion is called a "supernova". A star that went supernova
may shine for several weeks with an intensity equal to that of billions
Stars like the sun - its light may overshadow the light of the entire galaxy.

In 1054 a supernova exploded in a relatively close part of the galaxy
To the Earth - at a distance of 6,500 light years from it. Light of the explosion
It was so intense that Chinese astronomers described the "new star" that appeared
Suddenly they reported that three months after his appearance it was possible to distinguish
in its light during the day. The remnants of this explosion, known as the "Cancer Nebula",
They are one of the most beautiful celestial bodies known to us today.

Modern astrophysics teaches that supernovae are the melting pot
The cosmic where the hydrogen and helium, which make up most of the matter, were fused
In the universe, to heavier elements such as carbon, oxygen, nitrogen and iron.
The atoms that make up our planet and ourselves were created before me
billions of years, when an ancient star died in a supernova explosion.
In this sense, we are all made up of "stardust".

Aid in measuring distances in the universe

In recent years, the study of supernovae has aroused great interest not only in battle
The researchers of the evolution of the stars, but also among the cosmologists - the scientists
Those who study the structure of the universe, the mechanisms of its formation and the modes of its development.
The reason for this is the discovery that a certain type of supernova is uniform
Very: the amount of light emitted in explosions of this type is almost completely constant.
Such objects are called "standard candles", and they can help
Cosmologists have a task that sounds simple, but is actually very difficult:
measure distances.
When an astronomer observes an object that has very little light, it is very difficult for him to determine whether
It is a close object that emits little light, or a bright object that emits the least amount of light
that is received from him is due to the fact that he is very distant. It is similar to salt
The observer from the deck of a ship in a faint light flashes in the darkness: it is difficult for him to say
If it is the light of a small lantern mounted on top of a small fishing boat, it is foolish
near him, or the light of a powerful searchlight from a lighthouse on a distant shore.

If an astronomer observes a particular object, such as a supernova, which emits a quantity
A well-known light - that is, it is a "standard candle" - he can conclude
From the amount of light with which he measures the distance of the source. when discovered
A supernova that is a "standard candle" in a certain galaxy, can
Astronomers measure the distance to this galaxy with great precision. such measurements
Make it possible to map the distribution of galaxies and stars in the universe, and to draw conclusions from this
Very fundamental conclusions about the nature of the universe.

What can be learned from the distance of galaxies? To answer that we have to go back
to the beginning of the 20th century and the researches of the great astronomer Edwin Hubble.
As mentioned, until this period it was common to assume that the universe is eternal and immutable
variable. Hubble discovered that the universe is expanding: the galaxies he observed were moving away from each other
From here to everywhere. Moreover, Hubble discovered that the more the galaxy he observed
More distant, its speed away from us is higher. This important law,
On which modern cosmology is based, is called the "law of mourning".

To measure the distances to the galaxies he observed, Hubble used the stars
called "cupids", whose light intensity changes cyclically around a value
A certain average, so they can be calibrated as "standard candles". hall
This method is limited: cupid stars can only be detected in nearby galaxies
relatively. In more distant galaxies, the stars cannot be identified
the variables among the billions of stars that surround them. to continue the
The measurements using Hubble's method require a candle for larger distances
Brighter standard - like a supernova.

The expansion of the universe is accelerating

In the last three years, two international groups of
Astronomers - "The Cosmological Supernova Project" led by Dr. Shaul
Perlmutter of Lawrence Berkeley Laboratories in California, and a competing group led by him
of the Australian astronomer Brian Schmidt - measurements based on
Observations of very distant supernovae, which they discovered through the telescopes
The best we have today. From an analysis of the pine intensity of the supernovae
The distant ones and their comparison with nearby supernovae, is possible, if they are assumed to be
"Standard candles", to determine not only that the universe is expanding, but also if there is
A change in the rate of spread. The researchers calculated what she was likely to be
The brightness of distant supernovae if the universe is expanding at a constant rate. to him
The expansion of the universe was faster in the past, the researchers claimed, and meanwhile
Slowed down, after all the supernovae are supposed to be closer than expected,
and therefore also more clarity.

There is reason to expect such a slowdown: between all parts of the universe the force of gravity acts,
whose influence works to bring all the bodies in the universe closer together. the impact
The total force of gravity should therefore mean that the rate of expansion of the universe
Will go down. Because the strength of gravity weakens as the universe
spreads and the distance between all its parts increases, it is impossible to say for sure whether
Its influence will be strong enough to stop the expansion of the universe completely or not.
However, in any case, the researchers expected to find that the rate of spread was decreasing
And the supernovae are brighter.

To their surprise, both groups found, each separately, that the supernovae they had discovered
They were noticeably paler than he expected. The immediate conclusion from here
is that the expansion of the universe is accelerating: the rate of expansion of the universe today is greater than
its spread in the past. How can these results be explained? what causes
For the universe to accelerate, against the influence of gravity?

Members of both groups and many other cosmologists claim that the universe is indeed
spreads at an accelerated rate, and that in the universe there is a new component with strange properties,
which is responsible for accelerating the rate of expansion: this component is called "energy".
darkness". Other astronomers dispute the validity of these claims: it is possible,
They claim that the distant supernovae are paler because some
Mauren was engulfed by interstellar dust between us and them, or maybe
The supernovas are not "standard candles" at all.

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