Most Distant Detection Of Water In The Universe
Astronomers have found the most distant signs of water in the
Universe to date. The water vapour is thought to be contained in
a jet ejected from a supermassive black hole at the centre of a
galaxy, named MG J0414+0534
The image is made from HST data and shows the four lensed
images of the dusty red quasar, connected by a gravitational arc
of the quasar host galaxy. The lensing galaxy is seen in the
centre, between the four lensed images. (Credit: John McKean/HST
Archive data)
Dr John McKean of the Netherlands Institute for Radio Astronomy
(ASTRON) will be presenting the discovery at the European Week
of Astronomy and Space Science in Hatfield on Wednesday 22nd
April.
The water emission is seen as a maser, where molecules in the
gas amplify and emit beams of microwave radiation in much the
same way as a laser emits beams of light. The faint signal is
only detectable by using a technique called gravitational
lensing, where the gravity of a massive galaxy in the foreground
acts as a cosmic telescope, bending and magnifying light from
the distant galaxy to make a clover-leaf pattern of four images
of MG J0414+0534. The water maser was only detectable in the
brightest two of these images.
Dr McKean said, "We have been observing the water maser every
month since the detection and seen a steady signal with no
apparent change in the velocity of the water vapour in the data
we've obtained so far. This backs up our prediction that the
water is found in the jet from the supermassive black hole,
rather than the rotating disc of gas that surrounds it."
The radiation from the water maser was emitted when the Universe
was only about 2.5 billion years old, a fifth of its current
age.
"The radiation that we detected has taken 11.1 billion years to
reach the Earth. However, because the Universe has expanded like
an inflating balloon in that time, stretching out the distances
between points, the galaxy in which the water was detected is
about 19.8 billion light years away," explained Dr McKean.
Although since the initial discovery the team has looked at five
more systems that have not had water masers, they believe that
it is likely that there are many more similar systems in the
early Universe. Surveys of nearby galaxies have found that only
about 5% have powerful water masers associated with active
galactic nuclei. In addition, studies show that very powerful
water masers are extremely rare compared to their less luminous
counterparts. The water maser in MG J0414+0534 is about 10 000
times the luminosity of the Sun, which means that if water
masers were equally rare in the early Universe, the chances of
making this discovery would be improbably slight.
"We found a signal from a really powerful water maser in the
first system that we looked at using the gravitational lensing
technique. From what we know about the abundance of water masers
locally, we could calculate the probability of finding a water
maser as powerful as the one in MG J0414+0534 to be one in a
million from a single observation. This means that the abundance
of powerful water masers must be much higher in the distant
Universe than found locally because I’m sure we are just not
that lucky!" said Dr McKean.
The discovery of the water maser was made by a team led by Dr
Violette Impellizzeri using the 100-metre Effelsberg radio
telescope in Germany during July to September 2007. The
discovery was confirmed by observations with the Expanded Very
Large Array in the USA in September and October 2007. The team
included Alan Roy, Christian Henkel and Andreas Brunthaler, from
the Max Planck Institute for Radio Astronomy, Paola Castangia
from Cagliari Observatory and Olaf Wucknitz from the Argelander
Institute for Astronomy at Bonn University. The findings were
published in Nature in
December 2008.
The team is now analysing high-resolution data to find out how
close the water maser lies to the supermassive black hole, which
will give them new insights into the structure at the centre of
active galaxies in the early Universe.
"This detection of water in the early Universe may mean that
there is a higher abundance of dust and gas around the
super-massive black hole at these epochs, or it may be because
the black holes are more active, leading to the emission of more
powerful jets that can stimulate the emission of water masers.
We certainly know that the water vapour must be very hot and
dense for us to observe a maser, so right now we are trying to
establish what mechanism caused the gas to be so dense," said Dr
McKean.