The fastest nova starburst ever seen has been recorded by astronomers.
They watched as a white dwarf star ‘stole’ gas from a nearby red giant, triggering an explosion bright enough to be seen from Earth with binoculars.
Dubbed V1674 Hercules, the nova blast occurred 100 light-years away on June 12 last year, but lasted just a day — up to three times faster than any previously observed.
A nova is a sudden burst of bright light from a two-star system. Each nova is generated by a white dwarf — the very dense remaining core of a star — and a nearby companion star.
Arizona State University experts hope their observation will help answer bigger questions about the chemistry of our solar system, stellar deaths, and the evolution of the Universe.
The fastest nova starburst ever seen has been recorded by astronomers. This figure shows the type of two-star system to which the research team V1674 Hercules belongs
WHAT IS A WHITE DWARF?
A white dwarf is the remnant of a smaller star that has run out of nuclear fuel.
While large stars – those with more than ten times the mass of our Sun – suffer a spectacularly violent peak as a supernova explosion at the end of their lives, smaller stars are spared such dramatic fates.
As stars like the Sun reach the end of their lives, they exhaust their fuel, expand as red giants, and later eject their outer layers into space.
The hot and very dense core of the former star – a white dwarf – is all that remains.
White dwarfs are about the mass of the Sun but about the radius of Earth, meaning they’re incredibly dense.
The gravity on the surface of a white dwarf is 350,000 times that on Earth.
They get so dense because their electrons are smashed together, creating what caused “degenerative matter.”
This means that a more massive white dwarf will have a smaller radius than its less massive counterpart.
Material shot into space at speeds of millions of kilometers per hour – visible from Earth for just over 24 hours before fizzled out.
Lead author Professor Sumner Starrfield of Arizona State University said, “It was like someone turning a flashlight on and off.”
Novas are different from supernovas. They occur in binaries, in which there is a small, incredibly dense star and a much larger Sun-like companion.
The former, over time, drains matter from the latter, which falls on the white dwarf.
The white dwarf then heats this material, causing an uncontrolled reaction that releases a burst of energy and blasts the matter away at high speed, which we observe as visible light.
The bright nova usually fades over a few weeks or more, but V1674 Hercules was over in a day.
Professor Starrfield said: “It was only about a day, and the fastest nova so far was one we studied in 1991, V838 Herculis, which receded in about two or three days.”
Nova events at this rate are rare, making this nova a valuable study item.
Its speed wasn’t its only unusual feature – the light and energy it emits also pulses like the sound of an echoing bell.
There is a wobble every 501 seconds, detectable in visible light waves and X-rays. It’s still here a year later – and is set to last even longer.
Mark Wagner, chief scientist at the Large Binocular Telescope Observatory on Mount Graham in southern Arizona, said: “The most unusual thing is that this oscillation was seen before the eruption.
“But it was also evident when the nova was about 10 orders of magnitude brighter. A mystery that people are trying to wrestle with is what drives this periodicity that you would see over this range of brightnesses in the system.
The US team also noticed an odd wind as they monitored material ejected from the nova, which they think may depend on the positions of the white dwarf and its companion star.
They appear to shape the flow of material into the space surrounding the system that lay in the constellation of Hercules.
It is very conveniently placed as it is in a dark sky to the east as twilight fades after sunset.
Since it is less than 17° north of the celestial equator, it could be seen from anywhere in the world – and photographed with an exposure time of just a few seconds.
Novae can give us important information about our solar system and even the universe as a whole.
About 30 to 60 are thought to occur in the Milky Way each year, although only about 10 are discovered during this period. Most are obscured by interstellar dust.
A white dwarf gathers and alters matter, then flavors the surrounding space with new material as it goes nova.
It is an important part of the matter cycle in space, as the materials ejected by novae will eventually form new star systems.
Such events also contributed to the formation of our solar system and ensured that the earth is more than a lump of carbon.
White dwarfs are the incredibly dense remnants of Sun-sized stars after they have exhausted their nuclear fuel and shrunk to roughly the size of Earth (artist’s impression)
Professor Starrfield said: “We’re always trying to figure out how the solar system formed, where the chemical elements in the solar system come from.
“For example, one of the things we’re going to learn from this nova is how much lithium was produced in that explosion.
“We are now fairly certain that a significant portion of the lithium we have on Earth was produced by these types of explosions.”
Sometimes a white dwarf does not lose all of its accumulated matter during a nova explosion, so it gains mass with each cycle.
This would eventually make it unstable, and the white dwarf could produce a Type 1a supernova, which is one of the brightest events in the Universe.
Each type 1a supernova reaches the same brightness, so they are called standard candles.
Co-author Professor Charles Woodward of the University of Minnesota said: “Standard candles are so bright that we can see them from great distances across the universe.
“By looking at how the brightness of light changes, we can ask questions about the acceleration of the universe or the overall three-dimensional structure of the universe. This is one of the interesting reasons why we are studying some of these systems.’
In addition, novae can tell us more about how stars in binary systems evolve to death, a process that is not well understood.
They also function as living laboratories where scientists can see nuclear physics in action and test theoretical concepts.
The observed nova is now too faint for other types of telescopes, but it can still be monitored by the Large Binocular Telescope thanks to its large aperture and state-of-the-art scanners.
Professor Starrfield and colleagues now plan to study the cause, the processes that led to it, the reason for its record-breaking decline, the forces behind the observed wind, and the pulsating brightness.
The observation was published in the Research Notes of the American Astronomical Society.
HOW ARE STARS FORMED?
Stars form from dense molecular clouds — of dust and gas — in regions of interstellar space known as stellar nurseries.
A single molecular cloud, composed mostly of hydrogen atoms, can be thousands of times the mass of the Sun.
They undergo turbulent motion, with the gas and dust moving over time, disrupting the atoms and molecules, resulting in some regions having more matter than other parts.
When enough gas and dust gather in an area, it begins to collapse under the weight of its own gravity.
As it begins to collapse, it slowly gets hotter and expands outward, absorbing more of the surrounding gas and dust.
At that point, when the region is about 900 billion miles across, it becomes a prestellar core and the process of becoming a star begins.
Then, over the next 50,000 years, it will contract 92 billion miles in diameter to become the inner core of a star.
The excess material is flung toward the star’s poles, and a disk of gas and dust forms around the star, forming a protostar.
This matter is then either incorporated into the star or ejected into a wider disk leading to the formation of planets, moons, comets and asteroids.