According to new research at the University of Tokyo a fundamental change to the understanding of the Milky Way may be needed. An enormous region around the centre of the galaxy has been found to be devoid of new stars questioning previous beliefs about the distribution of these stars.
As Earth orbits the solar system, the solar system also orbits the galaxy. This journey around the Milky Way takes a galactic year and takes around 250 million Earth years. One galactic year ago, when Earth was last in the same position it is today, the dinosaurs walked the planet. This period was characterised by an exceptionally warm climate and was determined by the Solar system’s position. Usually, within the Milky Way young stars cluster in the spiral arms of the galaxy, when the Earth gets nearer to stars and supernovae, it may have powerful effects on the planet. Cosmic rays derive from these “new stars” and geological records show both the amount of cosmic rays and the temperature at times in the past, correspond with carbon-14 levels. This aims to show a clear one-to-one relationship between the two elements and the position of the solar system.
At the centre of almost all known galaxies is a black hole. The milky ways black hole Sagittarius A-star is millions of times bigger than the sun. This mysterious phenomenon eludes the absorption and emission of light, which makes it challenging to study. Black holes may contain dark matter which contributes 80% of all known matter in the Universe but so far only detected by its gravitational pull. All stars seem to orbit the centre of this attractive force. A more complete understanding of black holes may also be fundamental in the comprehension of the solar system’s origin and creation.
As a result of this gravitational pull the Milky Way is shaped as a spiral galaxy containing billions of stars from the centre to around 26,000 light years outwards. Young stars called Cepheid’s (10-300 million years old) pulsate in brightness and are believed to be important in the ability to measure the distribution of all stars in the Milky Way. Occurring in cycles, these pulsations may give clues as to how the Milky Way formed and evolved. Astronomers may decipher a Cepheid’s true brightness and in comparison with observations from Earth work out how far away it actually is. Previously, the pursuit of Cepheid’s in the centre of the Milky Way had been challenging because of outdated techniques and interstellar dust which obstructs their observation. It was previously believed Cepheid’s were evenly distributed around the galaxy.
A revision of the understanding of the Milky Way may now be needed according to a team of researchers at the University of Tokyo. The team consisting of Japanese, South African and Italian astronomers believe there may be an enormous region in the centre of the galaxy which is devoid of new stars. Using near-infrared observations with a telescope in Sutherland South Africa, it was found hardly any Cepheid’s exist in region extending 8000 light years from the core of the galaxy. “[It was] already found some while ago there are Cepheid’s in the central heart of the Milky Way (in a region about 150 light years in radius). Now it has been found outside this, there is a huge Cepheid desert extending out to 8000 light years from the centre,” says lead author Noriyuki Matsunaga.
These observations suggest the extreme inner disk is devoid of young stars. “The conclusions are contrary to other recent work, however in line with the work of radio astronomers observing an absence of new stars being born in this desert,” said co-author Michael Feast. The new results may stimulate new work into black holes and the nature of star formation. “The current results indicate there has been an absence of significant star formation in this large region over hundreds of millions of years. The movement and the chemical composition of the new Cepheid’s are helping to better understand the formation and evolution of the Milky Way,” said co-author Giuseppe Bono.
Why might Earth’s position within the Milky Way be relevant?