Read and translate Text 2.
Serious Blow to Dark Matter Theories?
New study finds mysterious lack of dark matter in
Sun’s neighbourhood
The most accurate study so far of the motions of stars in the Milky Way has found no evidence for dark matter in a large volume around the Sun. According to widely accepted theories, the solar neighbourhood was expected to be filled with dark matter, a mysterious invisible substance that can only be detected indirectly by the gravitational force it exerts. But a new study by a team of astronomers in Chile has found that these theories just do not fit the observational facts. This may mean that attempts to directly detect dark matter particles on Earth are unlikely to be successful.
A team using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, along with other telescopes, has mapped the motions of more than 400 stars up to 13 000 light-years from the Sun. From this new data they have calculated the mass of material in the vicinity of the Sun, in a volume four times larger than ever considered before.
“ The amount of mass that we derive matches very well with what we see – stars, dust and gas – in the region around the Sun,” says team leader Christian Moni Bidin (Departamento de Astronomía, Universidad de Concepción, Chile). “ But this leaves no room for the extra material – dark matter – that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there! ”
Dark matter is a mysterious substance that cannot be seen, but shows itself by its gravitational attraction for the material around it. This extra ingredient in the cosmos was originally suggested to explain why the outer parts of galaxies, including our own Milky Way, rotated so quickly, but dark matter now also forms an essential component of theories of how galaxies formed and evolved.
Today it is widely accepted that this dark component constitutes about the 80% of the mass in the Universe, despite the fact that it has resisted all attempts to clarify its nature, which remains obscure. All attempts so far to detect dark matter in laboratories on Earth have failed.
By very carefully measuring the motions of many stars, particularly those away from the plane of the Milky Way, the team could work backwards to deduce how much matter is present. The motions are a result of the mutual gravitational attraction of all the material, whether normal matter such as stars, or dark matter.
In their work, Moni Bidin et al. have looked at a sample of 400 red giant stars close to the Sun at vertical distances of 1.5 to 4 kpc above the MW disc. In addition to the stellar 3D positions, they have derived three-dimensional kinematics for these stars. From this data, they estimate the dynamical surface mass density of the MW within this range in heights from the disc. This surface mass density should be the sum of all mass, visible and dark. But it turns out, according to their analysis, that the visible mass alone is already a perfect fit to the observed value.
|
|
Astronomers’ existing models of how galaxies form and rotate suggest that the Milky Way is surrounded by a halo of dark matter. They are not able to precisely predict what shape this halo takes, but they do expect to find significant amounts in the region around the Sun. But only very unlikely shapes for the dark matter halo – such as a highly elongated form – can explain the lack of dark matter uncovered in the new study.
The new results also mean that attempts to detect dark matter on Earth by trying to spot the rare interactions between dark matter particles and “normal” matter are unlikely to be successful. (2984 symbols)
Notes
The MPG/ESO 2.2-metre telescope was originally constructed by the Max Planck Institute for Astronomy (Heidelberg, Germany) and intended to be sited in Namibia. It was not installed there and later offered to ESO under an agreement where ESO undertook the installation of the telescope at the La Silla Observatory in Chile – achieved in 1983 – and managed its subsequent operation. From 1 October 2013 ESO no longer offers the telescope to its users, although the Max Planck Society will continue to use it. The telescope and its instruments were also made available to Chilean astronomers and this will also continue in the future.
The telescope hosts three instruments: the 67-million pixel Wide Field Imager with a field of view as large as the full Moon, which has taken many amazing images of celestial objects; GROND, the Gamma-Ray Burst Optical/Near-Infrared Detector, which chases the afterglows of the most powerful explosions in the Universe, known as gamma-ray bursts; and the high-resolution spectrograph, FEROS, used to make detailed studies of stars.
Vocabulary list: ________________________________________________
so far – до сих пор; пока; до настоящего времени
accurate – точный
exert – вызывает, производит
Chile – Чили
derive – получать
attraction – притяжение
resist – противостоять, не поддаваться
obscure – смутный, неясный
backwards – в обратном направлении
et al. (лат.). – "и другие", "и прочие", "и все другие"
kpc = kiloparsec – кпк, килопарсек (астр. единица измерения космических расстояний, равная 1000 парсек.)
MW = Мilky Way – Млечный Путь
estimate – оценивать
halo [ˈheɪləʊ] – гало, кольцо вокруг планет,
|
|
elongated – вытянутый, удлинённый, продолговатый
Vocabulary Section
Exercise I. Find in the Text the English for:
самые точные исследования,пока что, широко распространенные теории, косвенным путем, которую он создает, не согласуется с наблюдаемыми фактами, вместе с другими, построить карту движений, вблизи, очень хорошо соответствует, не оставляет места, ее просто там нет (!), таинственное вещество, через гравитационное притяжение, внешние части галактик, важный компонент, не смотря на тот факт, что, образуются и развиваются, не поддается никаким попыткам, остается неясным, вернуться в начало, чтобы установить, взаимное притяжение, звезды типа "красный гигант", трех мерная кинематика, плоскость Млечного Пути, с большим разбросом высот над плоскостью, идеально согласовываться, окружен гало, необычная форма, очень вытянутая, отсутствие темной материи, попытки обнаружить.
Exercise II. Answer the following questions:
1. What did scientists expect to find around the Sun?
2. Have they found it?
3. What did a team of Chilean astronomers study?
4. What equipment did they use in their observations?
5. What were the results of their observations?
6. Why did scientists suggest the existence of dark matter?
7. What do astronomers suppose about dark matter?
8. What did the measuring of surface mass density testify of?
9. How can the form of halo explain the lack of dark matter?
10. Does it mean that there is no dark matter at all?
Exercise III. Render in English:
Куда дели темную материю?
Наблюдения, проведенные в Европейской южной обсерватории, показали, что в окрестностях Солнца очень мало темной материи. Вообще, темная материя должна занимать около 83% всей массы Вселенной. Плотность темной материи в ближайшей галактической окрестности Солнца при этом должна составлять около 0.5 килограмм на объем земного шара, но новые данные указывают на количество не более 60 грамм, а скорее и того меньше.
|
|
Группа астрономов под руководством Кристиана Мони Бидин из Университета Консепсьона использовала телескоп MPG/ESO для наблюдения динамики более чем 400 звезд, находящихся на расстояния не более 13000 световых лет от нас. Это позволило провести оценку плотности в пространстве, превышающем предыдущие в четыре раза. «Количество массы, которое мы получили, хорошо согласуется с тем количеством вещества, которое мы наблюдаем в форме звезд, пыли и газа в околосолнечном пространстве, – говорит Бидин. – Но, выходит, у нас нет места для темной материи, которую мы и рассчитывали найти. Согласно нашим ожиданиям, темная материя должна была ярко проявиться в наших наблюдениях. Но ее там просто не оказалось!»
Современные модели структуры нашей галактики говорят о том, что околосолнечная область заполнена темной материей. Новое исследование показывает, что либо вообще представление о темной материи неверно, либо форма гало темной материи очень специфическая, но все же укладывающаяся в современную теорию. Также новый результат указывает на то, что нет смысла пытаться определить свойства частиц темной материи по их взаимодействию с материей на Земле.
(Космос-Журнал
по материалам Европейской южной обсерватории)