Source: The Daily Galaxy
A team of NASA and European scientists recorded the "fingerprints" of
mystery molecules this summer in two distant galaxies, Andromeda and the
Triangulum. Astronomers can count on one hand the number of galaxies
examined so far for such fingerprints, which are thought to belong to
large organic molecules (molecules that have at least 20 atoms or more),
says the team's leader, Martin Cordiner of NASA's Goddard Center for
Astrobiology. This is quite small compared to, say, a protein, but huge
compared to a molecule of carbon monoxide, a very common molecule in
space.
Figuring out exactly which molecules are leaving these clues, known as
"diffuse interstellar bands" (DIBs), is a puzzle that initially seemed
straightforward but has gone unsolved for nearly a hundred years. The
answer is expected to help explain how stars, planets and life form, so
settling the matter is as important to astronomers who specialize in
chemistry and biology as determining the nature of dark matter is to the
specialists in physics.
The findings provide some evidence
against one of the top candidates on the list of suspects: polycyclic
aromatic hydrocarbons (PAHs), a group of molecules that is widespread in
space. The research also reveals that some of the signatures found in
Andromeda and the Triangulum are similar to ones seen in our own Milky
Way, despite some big differences between those galaxies and ours."We have studied DIBs in incredibly diverse environments. Some have low levels of UV radiation. Some have radiation levels thousands of times higher. Some have different amounts of 'ingredients' available for making stars and planets," Cordiner says. "And throughout all of these, we see DIBs."
Until now, only two galaxies beyond our own have been investigated in detail for DIBs. Those are our nearest neighbors, the Large and Small Magellanic Clouds, which lie 160,000 to 200,000 light years away. Andromeda and the Triangulum are located much farther away, at about 2.5 to 3 million light years from Earth. "At those distances, individual stars are so faint that we need to push even the largest telescopes in the world to their limits in order to observe them," Cordiner says.
To effectively study DIBs, researchers have to pick out individual stars
within the galaxy, and only a few telescopes worldwide are powerful
enough to gather sufficient light for that, which is why most DIBs found
so far have been in the Milky Way. (The team used the Gemini
Observatory's telescope in Hawaii.)
"The first step is choosing which stars to observe," Cordiner explains. Cordiner's colleagues at Queen's University in Belfast, U.K., took the lead on finding good targets. They picked blue supergiants—stars that are very large, very hot and very bright. Supergiants also burn very clean: unlike our sun and other cooler stars, they contribute little background clutter to the observations being made.
In the image above, The Triangulum Galaxy, located nearly 3 million light years from Earth, is another far galaxy where researchers have found diffuse interstellar bands (DIBs). The detailed observations needed to see DIBs along a straight line from Earth to an individual star in such a distant galaxy stretch the limits of even the largest telescopes.
To look for DIBs, an astronomer points the telescope at a star and scans through a rainbow made up of thousands of wavelengths of light. This rainbow, or spectrum, is extended a bit beyond visible light, into the UV at the blue end and into the infrared at the red end.
DIBs are not defined by what astronomers see while doing this, but by what they don't see. The colors missing from the rainbow, marked by black stripes, are the ones of interest. Each one is a wavelength being absorbed by some kind of atom or molecule.
A DIB is one of these regions where the color is missing. But compared to the nice, neat "absorption lines" that are identified with atoms or simple molecules, a DIB is not well-behaved, which is why it stands out.
"Astronomers were used to seeing quite sharp, narrow bands where typical atoms and molecules absorb," says Cordiner. "But DIBs are broad; that's why they are called 'diffuse.' Some DIBs have simple shapes and are quite smooth, but others have bumps and wiggles and may even be lopsided."
"The first step is choosing which stars to observe," Cordiner explains. Cordiner's colleagues at Queen's University in Belfast, U.K., took the lead on finding good targets. They picked blue supergiants—stars that are very large, very hot and very bright. Supergiants also burn very clean: unlike our sun and other cooler stars, they contribute little background clutter to the observations being made.
In the image above, The Triangulum Galaxy, located nearly 3 million light years from Earth, is another far galaxy where researchers have found diffuse interstellar bands (DIBs). The detailed observations needed to see DIBs along a straight line from Earth to an individual star in such a distant galaxy stretch the limits of even the largest telescopes.
To look for DIBs, an astronomer points the telescope at a star and scans through a rainbow made up of thousands of wavelengths of light. This rainbow, or spectrum, is extended a bit beyond visible light, into the UV at the blue end and into the infrared at the red end.
DIBs are not defined by what astronomers see while doing this, but by what they don't see. The colors missing from the rainbow, marked by black stripes, are the ones of interest. Each one is a wavelength being absorbed by some kind of atom or molecule.
A DIB is one of these regions where the color is missing. But compared to the nice, neat "absorption lines" that are identified with atoms or simple molecules, a DIB is not well-behaved, which is why it stands out.
"Astronomers were used to seeing quite sharp, narrow bands where typical atoms and molecules absorb," says Cordiner. "But DIBs are broad; that's why they are called 'diffuse.' Some DIBs have simple shapes and are quite smooth, but others have bumps and wiggles and may even be lopsided."
