Meet the two-faced star! Bizarre white dwarf has one side made of hydrogen and the other made of helium – and astronomers are absolutely baffled
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Astronomers have been ‘baffled’ by the discovery of a star with two faces – one side made of hydrogen and the other of helium.
Nicknamed Janus after the two-faced Roman god of transition, the helium side has a gritty or “bubbly” appearance, while the hydrogen side is smoother and brighter.
Janus, which is more than 1,000 light-years away in the constellation Cygnus, performs an ultrafast rotation on its axis every 15 minutes, causing it to flash across the night sky.
The object’s temperature is a scorching 35,000 Kelvin (equivalent to 63,000 °F or 35,000 °C) – about six times hotter than the surface of our sun.
It follows the discovery of the hottest known brown dwarf to date, a strange planet-star hybrid, about 2200 kilometers away.
In a first for white dwarfs, the burned-out cores of dead stars, astronomers have discovered that at least one member of this cosmic family has two faces. One side of the white dwarf is hydrogen, while the other is helium. In the photo, an artist’s concept, with the hydrogen side appearing brighter on the right
Janus, which was found with the Zwicky Transient Facility (ZTF) in California, has been detailed in a new study led by astronomers at the California Institute of Technology (Caltech).
“The surface of the white dwarf changes completely from one side to the other,” said lead study author Ilaria Caiazzo, a postdoctoral researcher at Caltech.
“When I show the sightings to people, they are blown away.”
The team is “baffled” at how a white dwarf floating alone in space could have such different sides, but they’ve come up with some possible theories.
Its special nature could be due to the presence of a small magnetic field, which causes ‘an inhomogeneity’ in temperature or pressure on the surface.
White dwarfs are the incredibly dense stellar remnants or “corpses” of dead stars after they’ve exhausted their nuclear fuel, shrinking to about the size of Earth.
About 98 percent of all the stars in the universe will eventually become white dwarfs, including our own sun.
Most white dwarfs have hydrogen-rich atmospheres because as they form, their heavier elements sink to their cores and their lighter elements — hydrogen being the lightest of them all — float to the top.
But over time, as white dwarfs cool, the materials are believed to mix.
if you could get close enough to see it the helium side would look gritty or ‘bubble’ while the hydrogen side would look smoother and brighter
Janus was found with the Zwicky Transient Facility (ZTF, pictured), a large-scale astronomical survey of the California sky
In some cases, the hydrogen is mixed into the interior and diluted so that helium is more common.
Janus may be going through this transition phase, but that doesn’t explain why the transition happens in a disjointed fashion, with one side evolving before the other.
The answer to this could be magnetic fields, which are usually stronger on one side of a cosmic body.
Another possible answer is that we may be witnessing Janus going through a rare phase of white dwarf evolution.
“Not all, but some white dwarfs are transitioning from being hydrogen-dominated to helium-dominated on their surfaces,” Caiazzo said.
“Maybe we caught a white dwarf in the act.”
Janus was initially discovered by Caiazzo, who was looking for highly magnetized white dwarfs, such as the object known as ZTF J1901+1458, which she and her team had previously found using ZTF.
Janus performs an ultra-fast rotation on its axis, making it appear to flash in the night sky. Pictured, light emission from the star with a period of 14.97 minutes
Officially known as ZTF J203349.8+322901.1, Janus was notable for its rapid changes in brightness due to its super-fast rotation around its axis.
Caiazzo did further research with Caltech’s CHIMERA instrument, a photometer (a device that measures the strength of electromagnetic radiation).
Researchers also studied data from HiPERCAM, an optical imager on the Gran Telescopio Canarias in Spain’s Canary Islands.
Data confirmed that Janus rotates on its axis every 14.97 minutes – an instant compared to our sun’s rotation (once every 27 days).
Later observations with the WM Keck Observatory atop Maunakea in Hawaiʻi revealed the dual nature of the white dwarf.
The team then used an instrument called a spectrometer to scatter the white dwarf’s light into a rainbow of wavelengths containing chemical fingerprints.
Data revealed the presence of hydrogen when one side of the object was in view (with no signs of helium), and only helium when the other side swung into view.
On the helium side, which appears effervescent, convection has destroyed the thin layer of hydrogen on the surface and brought up the helium below
The discovery was made by the Zwicky Transient Facility (ZTF), which operates at Caltech’s Palomar Observatory, using two telescopes in Hawaii – one on the island of Maui and the WM Keck Observatory on Maunakea (pictured)
According to the experts, this new class of white dwarfs could shed light on the physical mechanisms behind their evolution.
Like other white dwarfs, Janus cools down until it becomes a black dwarf, a “stellar remnant” that emits neither light nor heat.
Eventually, black dwarfs cool to absolute zero — the lowest temperature theoretically possible — and become invisible.
Since the time it takes for a white dwarf to reach this state is believed to be longer than the current age of the universe (13.8 billion years), no black dwarfs are expected to exist in the universe at this time.
The new study is published in the journal Nature.
WHAT HAPPENS TO THE EARTH WHEN THE SUN DIES?
It is said that in five billion years the sun will have grown into a red giant star, more than a hundred times larger than its current size.
Eventually it will eject gas and dust to create an “envelope” that represents as much as half of its mass.
The core will become a small white dwarf star. This will shine for thousands of years and illuminate the envelope to create an annular planetary nebula.
It is said that in five billion years the sun will have grown into a red giant star, more than a hundred times larger than its current size
While this metamorphosis will change the solar system, scientists aren’t sure what will happen to the third stone from the sun.
We already know that our sun will be bigger and brighter, so it will likely wipe out any form of life on our planet.
But whether Earth’s rocky core will survive is uncertain.