A strange two-faced star has been discovered by astronomers – made of hydrogen on one side and helium on the other.
The newfound white dwarf has been nicknamed Janus – after the Roman god of transition.
Dr. Caiazzi explained: “Not all, but some white dwarfs transition from being hydrogen to helium-dominated on their surface.
The blue-tinted star is composed mainly of hydrogen on one side and helium on the other. The former appears brighter.
The phenomenon might be due to a mixing of materials, known as convection.
On the helium side, which appears bubbly, the thin hydrogen layer on the surface has been destroyed – bringing up the helium underneath.
White dwarfs are the scalding remains of stars that were once like our sun. As the stars age, they puff up into red giants.
Eventually, their outer fluffy material is blown away and their cores contract into dense, fiery-hot white dwarfs. Our sun will evolve into a white dwarf in about five billion years.
Janus was detected by a scanner called ZTF (Zwicky Transient Facility) at the Palomar Observatory near San Diego.
Dr. Caiazzo had been searching for highly magnetized white dwarfs which she and her team found previously using the device.
Further investigations showed Janus is rotating on its axis every 15 minutes – and revealed the dramatic double-faced nature of the white dwarf.
The researchers used a spectrometer to spread the light of the white dwarf into a rainbow of wavelengths that contain chemical fingerprints.
But over time, as the white dwarfs cool, the materials are thought to mix together.
In some cases, the hydrogen is mixed into the interior and diluted such that helium becomes more prevalent.
One side may evolve before the other due to magnetic fields.
On the other hand the fields may change the pressure and density of the atmospheric gases.
Co-author Professor James Fuller, also from Caltech, said: “The magnetic fields may lead to lower gas pressures in the atmosphere and this may allow a hydrogen ‘ocean’ to form where the magnetic fields are strongest.
Dr. Caiazzo said: “ZTF is very good at finding strange objects.” Future surveys should make finding variable white dwarfs even easier.
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