Galactic archaeology reveals supermassive black hole caused 'dramatic explosion'

The work of galactic archaeologists is to sift through stellar fossil records to uncover the history of our universe. As traditional archaeologists study human history by investigating the traces and remains of previous civilisations, so galactic archaeologists trace the history and formation of the Milky Way and other galaxies by observing traces of stars that are billions of years old.

Speaking to IBTimes UK, Professor Joseph Silk said the history of the galaxy was, in essence, the search for fossils. "To probe back in time, one can look in our vicinity for the oldest stars," he said. A leading expert on the early universe and the author of The Infinite Cosmos, Silk explained the science behind. galactic archaeology. "Our galaxy is teeming with white dwarfs [a stellar remnant], testimony that intense episodes of star formation and death occurred billions of years ago. Long-dead massive stars leave chemical imprints in low mass stars like our sun."

In a few decades, scientists may be able to solve one of the biggest mysteries in the universe – the black hole – which is formed when a massive star dies. The new Lisa Pathfinder satellite, launched by the European Space Agency on 3 December, will allow astronomers to "see" black holes for the first time. The satellite has special sensors that can detect gravity waves, which are a phenomena predicted by Einstein's theory of general relativity.

"A few million years ago, there was a dramatic explosion at the centre of our galaxy," Professor Silk said. "The centre of our Milky Way contains the nearest supermassive black hole, and is the only plausible source for the explosion."

Advances in science and technology are improving our understanding of the universe. Just 30 years ago, it was assumed that stars born in disks did not move far from their original place of origin. It was thought that stars stayed put for most of their lives, but recent work on galactic disk dynamics shows that this theory is flawed. Recent research shows that stars wander considerable distances through their lives in a process of radial migration that affects the entire galactic disk.

The search for alien life

One of the key questions is how galactic archaeology can help us learn if there are other forms of life out there. Most astrophysicists accept a high probability of there being life elsewhere in the universe. The Kepler Mission is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone. To locate them, telescopes is look for transits – times when terrestrial-size planets cross in front of their star, temporarily darkening it. If the darkening is just the right amount, and happens on a regular schedule, that could be evidence of an Earth-sized world.

According to Silk: "We're still a long way from finding Earth-like planets. People are busy designing new technology which is designed to eventually image Earth-like twins, roughly in the habitable zone. That's the hope and I would guess in 10 or 20 years we will follow them up and then zero in on these candidate Earth-like planets and see if there are any indications of life and that is a very controversial and difficult subject. The origins of life are so complicated that it cannot predict whether it happened once or billions of times."

Stars roving around the universe

A new map of the Milky Way has revealed that of all the stars in our galaxy, nearly a third have moved far from their stellar birthplace. The discovery was made by astronomers using the Sloan Digital Sky Survey-III (SDSS), which spectroscopically linked chemical elements in stars with the locations in our galaxy known to be abundant in those specific elements.

"We were able to measure the properties of nearly 70,000 stars in our galaxy for this particular study using the innovative SDSS infrared spectrograph," said astronomer Donald Schneider, of Penn State University. "This exercise can be described as galactic archaeology. These data reveal the locations, motions and compositions of the stars, which provide insights into their formation and their history."

"In our modern world, many people move far away from their birthplaces, sometimes halfway around the world," said Michael Hayden from New Mexico State University (NMSU) and lead author of a study published in the Astrophysical Journal. "Now we're finding the same is true of stars in our galaxy. About 30% of the stars in our galaxy have traveled a long way from where they were born."

Intergalactic equipment

Over the past 10 years, a new technique has been used that picks out the primitive stars more efficiently. Using large prisms attached to the front of telescopes, astronomers have recorded the spectra of many objects at once. As stars are created and eventually die, heavier elements are can be found in the atmospheres of each progressive stellar population. The spectroscopic signature of any given star acts like rings which are used to age a tree. For stars, the chemical fingerprint in their atmospheres can also reveal where and when they formed in our galaxy.

"Stellar spectra show us that the chemical makeup of our galaxy is constantly changing," said astronomer Jon Holtzman, of New Mexico State University (NMSU). "Stars create heavier elements in their cores, and when the stars die, those heavier elements go back into the gas from which the next stars form."

With the latest high-speed computers, it is now possible to recognise the spectrum of a star and to find the most primitive ones. A new search of this type, based on spectra taken as part of the Hamburg/ESO (European Southern Observatory) spectral study, is now being undertaken by Dr Norbert Christlieb of the Hamburger Sternwarte as well as other scientists around the world.

Set to launch in 2018 is the world's biggest telescope. Built by Nasa, the James Webb Space Telescope will be 100 times more powerful than the Hubble Space Telescope. It will give scientists the opportunity to "see" cosmic events that occurred 13.5bn years ago – just 220m years after the Big Bang.

"What the Webb will really be doing is looking at the first galaxies of the Universe," project scientist Mark Clampin said during a press conference at Nasa's Goddard Space Flight Centre. "We will also be able, with these capabilities, to look in very dark parts of the universe where stars are being born."