Credits By: CALTECH
Astronomers have found that at least one member of the cosmic family known as white dwarfs, the burnt-out cores of dead stars, has two faces. The white dwarf has two halves, one formed of hydrogen and the other of helium.
“The surface of the white dwarf completely changes from one side to the other,” claims Ilaria Caiazzo, a postdoctoral researcher at Caltech who is the primary author of a new article on the results published in Nature. The reactions of those I reveal the observations to are astounding.
The scorching remains of stars that formerly resembled our sun are white dwarfs. The stars develop into red giants as they grow older. Eventually, the outer, fluffy material is blown away, and the cores of the stars eventually become dense, incredibly hot white dwarfs. In roughly 5 billion years, our sun will change into a white dwarf.
The Zwicky Transient Facility (ZTF), an instrument that monitors the skies every night from Caltech’s Palomar Observatory in San Diego, made the first discovery of the newly discovered white dwarf, which has been given the name Janus after the two-faced Roman deity of transition. Caiazzo had been looking for strongly magnetised white dwarfs like the ZTF J1901+1458 object she and her team discovered earlier using ZTF. Caiazzo conducted more research using the CHIMAERA instrument at Palomar and HiPERCAM on the Gran Telescopio Canarias in Spain’s Canary Islands after one candidate object stood out for its rapid brightness variations. These findings demonstrated that Janus rotates on its axis once every fifteen minutes.
The stunning double-faced Nature of the white dwarf was discovered through further observations taken with the W. M. Keck Observatory on top of Maunakea in Hawaii. The team split the white dwarf’s radiation into a spectrum of wavelengths with distinct chemical signatures using a device known as a spectrometer. When just one side of the object was visible, the data showed hydrogen to be there (but no indication of helium) and only helium when the other side came into view.
Why would a white dwarf fly alone in space have two sides that are so radically different? Though they admit to being perplexed, the team has developed some hypotheses. One theory is that we could see a unique stage in the evolution of white dwarfs on Janus.
Some white dwarfs, though not all, go from having hydrogen- to helium-dominated surfaces, according to Caiazzo. We may have observed one such white dwarf in action.
After white dwarfs are created, their lighter atoms—hydrogen being the weakest of all—float to the surface while their heavier elements sink to their cores. However, the materials are believed to eventually combine as the white dwarfs cool down. In some instances, the hydrogen is diluted and mixed with the interior, which causes helium to predominate. Janus may represent this time of transition, but a critical point needs to be answered: why is the change occurring so unevenly, with one side developing before the other?
According to the scientific team, magnetic fields might be the solution’s key.
“Magnetic fields around cosmic bodies tend to be asymmetric or stronger on one side,” says Caiazzo. “Magnetic fields can stop materials from combining. Therefore, if the magnetic field is stronger on one side, there will be less mixing and more hydrogen.
The team’s second explanation for the two faces relies on magnetic fields. However, in this case, it is hypothesised that the areas will alter the pressure and density of the atmospheric gases.
According to co-author James Fuller, professor of theoretical astrophysics at Caltech, “The magnetic fields may result in lower gas pressures in the atmosphere, and this may allow a hydrogen “ocean” to emerge where the magnetic fields are highest. Although we are still determining which of these
hypotheses is accurate, we cannot come up with any other explanations for the asymmetric sides save magnetic fields.
The team wants to use ZTF’s sky survey to identify more white dwarfs resembling Janus to answer the enigma. ZTF excels at locating unusual items, claims Caiazzo. She claims that further surveys, such as those to be carried out by the Vera C. Rubin Observatory in Chile, should make locating fluctuating white dwarfs even simpler.
The study, titled “A rotating white dwarf shows different compositions on its opposite faces,” was supported by the European Research Council, the Leverhulme Trust, and the Science and Technology Facilities Council of the United Kingdom. It was conducted at the Walter Burke Institute for Theoretical Physics at Caltech.
The study also used data from NASA’s Neils Gehrels Swift Observatory, renamed in honour of Gehrels, a Caltech graduate (PhD 82) who died away in 2017. This data allowed the object’s temperature to be pinpointed to a scorching 35,000 Kelvin or around 35,000 degrees Celsius.
The National Science Foundation and a global partnership of partners support Caltech’s ZTF. Caltech and the Heising-Simons Foundation both contribute additional funding. IPAC, a science and data centre for astronomy at Caltech, processes and stores ZTF data. With the help of the Near-Earth Object Observations programme, NASA assists ZTF in its hunt for near-Earth objects.
