Astronomers have been “baffled” by the discovery of a two-sided star – with one side made up of hydrogen and the other made up of helium.
Nicknamed Janus after the two-faced Roman god of transition, its helium side has a grainy or “bubbly” look, while the hydrogen side is smoother and shinier.
Janus, which lies over 1,000 light-years away in the constellation Cygnus, rotates lightning-fast on its axis every 15 minutes, causing it to flash across the night sky.
The object’s temperature is 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 brown dwarf known to datea strange planet-star hybrid, located about 1,400 light-years away.
In a first for white dwarfs, the scorched 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 made up of hydrogen, while the other is made up of helium. Pictured is an artist’s concept, with the hydrogen side on the right appearing brighter
Janus, which was found with the Zwicky Transient Facility (ZTF) in California, has been detailed in a new study by astronomers from the California Institute of Technology (Caltech).
“The surface of the white dwarf changes completely from side to side,” said the study’s lead author, Ilaria Caiazzo, a postdoctoral researcher at Caltech.
“When I show the sightings to people, they are blown away.”
The team is “baffled” as to how a white dwarf floating alone in space would have such different sides, but they came up with a few possible theories.
Its peculiar nature could be caused by the presence of a small magnetic field, which creates an “inhomogeneity” of temperature or pressure on the surface.
White dwarfs are the incredibly dense stellar remnants or “corpses” of stars that have died after exhausting their nuclear fuel, shrunk to about the size of Earth.
About 98% of all stars in the universe will eventually become white dwarfs, including our own sun.
Most white dwarfs have a hydrogen-rich atmosphere because as they form, their heavier elements sink to their core and their lighter elements – hydrogen being the lightest of all – float upwards.
But over time, as the white dwarfs cool, the materials are thought to mix together.
if you could get close enough to see it, its helium side would look grainy or “bubbly”, while the hydrogen side would appear smoother and brighter
Janus was found with the Zwicky Transient Facility (ZTF, pictured), a wide-field astronomical survey of the sky in California
What is a white dwarf?
A white dwarf is the remnant of a small star that has run out of nuclear fuel.
As stars age, they swell into red giants; eventually their outer fluffy matter is blown away and their cores contract into dense, burning white dwarfs.
Our sun will evolve into a white dwarf in about 5 billion years.
In some cases, hydrogen is mixed in and diluted so that helium becomes more prevalent.
Janus may be going through this phase of transition, but that doesn’t explain why the transition occurs in a disjointed fashion, with one side moving before the other.
The answer to this could be magnetic fields, which tend to be strongest on one side of a cosmic body.
Another possible answer is that we may be witnessing Janus undergoing a rare phase of white dwarf evolution.
“Not all, but some white dwarfs change from hydrogen to helium on their surface,” Caiazzo said.
“We might have caught one of these white dwarfs in the act. »
Janus was originally 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 previously found using ZTF.
Janus rotates lightning-fast on its axis – making it appear like a flash in the night sky. In the photo, light emission from the star at a period of 14.97 minutes
Officially known as ZTF J203349.8+322901.1, Janus stood out for its rapid changes in brightness, due to its ultra-fast rotation on its axis.
Caiazzo furthered his research with Caltech’s CHIMERA instrument, which is a photometer (a device that measures the strength of electromagnetic radiation).
The researchers also studied data from HiPERCAM, an optical imager on the Gran Telescopio Canarias in Spain’s Canary Islands.
The data confirmed that Janus rotates on its axis every 14.97 minutes – a blink of an eye compared to the rotation of our sun (once every 27 days).
Later observations made with the WM Keck Observatory atop Maunakea in Hawaii revealed the double-sided nature of the white dwarf.
The team then used an instrument called a spectrometer to scatter light from the white dwarf into a rainbow of wavelengths containing chemical fingerprints.
The data revealed the presence of hydrogen when one side of the object was in view (with no sign of helium), and only helium when the other side came into view.
On the helium side, which looks fizzy, convection has destroyed the thin layer of hydrogen on the surface and pushed the helium up below
The discovery was made by the Zwicky Transient Facility (ZTF), which operates at Caltech’s Palomar Observatory, with help from two telescopes in Hawaii – one on the island of Maui and the WM Keck Observatory on Maunakea (pictured)
According to experts, this new class of white dwarfs could help shed light on the physical mechanisms behind their evolution.
Just like other white dwarfs, Janus will cool down until it becomes a black dwarf, a “stellar remnant” that emits no light or heat.
Eventually, the black dwarfs cool down to absolute zero – the lowest temperature theoretically possible – and become invisible.
As 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 present.
The new study has been published in the journal Nature.
In five billion years, the Sun is said to have become 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” of up to half its mass.
The core will become a tiny white dwarf star. It will glow for thousands of years, illuminating the envelope to create a ring-shaped planetary nebula.
In five billion years, the Sun is said to have become a red giant, more than a hundred times larger than its current size.
While this metamorphosis will change the solar system, scientists don’t know what will happen to the third rock from the Sun.
We already know that our Sun will be bigger and brighter, so it will likely destroy all life on our planet.
But the survival of the rocky core of the Earth is uncertain.