Artist’s impression of a very distant quasar powered by a black hole with a mass two billion times that of the Sun. (Image: ESO/M. Kornmesser via Wikimedia Commons)

Scientists have found the largest known structure in the universe, a cluster of galactic cores so vast it would take four billion years for a spacecraft traveling at the speed of light to cross it.

The sighting challenges a theory from Einstein which suggests such a massive object shouldn’t exist in the universe.

A quasar is the compacted center of a galaxy surrounding a massive black hole from the early days of the universe.  Quasars  go through periods of extreme brightness which can last anywhere from 10 to 100 million years. They tend to band together in enormous clusters, or structures, forming large quasar groups (LQGs).

The international group of scientists led by Roger Clowes from the University of Central Lancashire’s Jeremiah Horrocks Institute, used data from the Sloan Digital Sky Survey (SDSS), a major surveying project that uses 2.5-m wide-angle optical telescope located at New Mexico’s Apache Point Observatory, to make their findings.

Clowes and his colleagues are astounded by the size of this structure, which defies the Cosmological Principal, based on Albert Einstein’s theory of General Relativity that assumes when you look at the universe from a sufficiently large scale; it looks the same no matter where you are observing it from.  The Cosmological Principle, according to the research team, is assumed but has never been demonstrated observationally ‘beyond reasonable doubt.’

Large quasar group (LQG) as imaged by the Big Throughput Camera at the Cerro Tololo Inter-American Observatory in Chile (Photo: Chris Haines)

“While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire universe,” said Clowes. “This is hugely exciting, not least because it runs counter to our current understanding of the universe. The universe doesn’t seem to be as uniform as we thought.”

Clusters of galaxies can be anywhere from six to 10 million light-years across, but the LQGs can be 650 million light-years or more across. Making calculations based on the Cosmological Principle, along with the modern theory of cosmology, astrophysicists shouldn’t be able to find a structure in the universe larger than 1.2 billion light-years, much less four billion light-years across as this newly sighted structure is.

To get some additional perspective of what the astronomers found, let’s step back and give it a sense of scale.  Our own galaxy, the Milky Way, is separated from its nearest neighbor, the Andromeda Galaxy, by a distance of 2.5 million light-years.

Clowes points out that his team’s discovery does have a typical dimension of 1.6 billion light-years. But, because it is elongated, its longest dimension is four billion light-years, making it about 1,650 times larger than the distance from the Milky Way to Andromeda.

The newly discovered planet PH1 is depicted in this artist’s rendition transiting the larger of the its two host stars. Left of the planet, off in the distance, is a second pair of stars that orbit PH1. (Image: Haven Giguere/Yale)

The recent discovery of a four-star planet highlights the growing value of citizen scientists, non-professional enthusiasts – including  hobbyists, educators and amateur scientists – who participate in scientific endeavors.

The discovery of the extrasolar planet dubbed PH1, which orbits twin suns and is itself orbited by a second distant pair of stars, was made through the combined efforts of volunteer citizen scientists and  professional astronomers.

The amateur scientists behind the sighting of the phenomenon, called a “circumbinary planet in a four-star system,” were able to get involved with astronomical research through the website Planethunters.org, a collaboration between Yale University and the online citizen science project Zooniverse.

“Planet Hunters is a symbiotic project, pairing the discovery power of the people with follow-up by a team of astronomers,” says Debra Fischer, a planet expert and professor of astronomy at Yale, who helped launch the website in 2010. “This unique system might have been entirely missed if not for the sharp eyes of the public.”

Through Planethunters.org, volunteers help professional astronomers sift through mountains of data  gathered by NASA’s Kepler space mission.

That assistance includes brightness measurements, or “light curves,” for more than 150,000 stars, taken by instruments aboard Kepler  every 30 minutes.

Artist’s rendition of the newly discovered circumbinary planet PH1 that orbits two suns (upper left) and is 5,000 light years from Earth. (Image: Haven Giguere/Yale)

The Planet Hunters pour through the data looking for possible transit events, a brief dip in brightness that occurs when a planet or other celestial body passes in front of the star.

“The thousands of people who are involved with Planet Hunters are performing a valuable service,” says Jerome Orosz, associate professor of astronomy at San Diego State University and co-author of the paper outlining PH1’s discovery. “Many of the automated techniques used to find interesting features in the Kepler data don’t always work as efficiently as we would like. The hard work of the Planet Hunters helps ensure that important discoveries are not falling through the cracks.”

PH1, some 5000 light years from Earth, has been described by astronomers as a gas giant planet slightly bigger than Neptune.  It takes the extrasolar planet 138 days to complete an orbit around its two host stars, which have masses about 1.5 and 0.41 times that of the sun and also circle each other once every 20 days.  The two distant stars that orbit the new-found planet are about 144,840,960,000 km away, roughly 1000 times the distance between the Earth and the Sun.

Yale’s Meg Schwamb of Yale, the lead author of the paper said that the circumbinary planets that are being discovered are the extremes of planet formation.

“The discovery of these systems is forcing us to go back to the drawing board to understand how such planets can assemble and evolve in these dynamically challenging environments.”