There Might Be a Planet Orbiting a Cruel Dead Star, And Now We Know How To Find Them

Have you heard of the LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis? No, they weren’t in the boy band in ancient Rome. They are Cataclysmic Variables, binary stars so close together that one star takes matter from its sibling. This causes the pairs to vary greatly in brightness.

Could a planet exist in this chaotic environment? Can we see them? A new study says yes to both.

Cataclysmic Variables (CVs) experienced a large increase in brightness. All stars vary in brightness to some degree, even our own sun. But the CV increase in brightness is much more pronounced than in stars like our Sun, and it happens on an irregular basis

There are different types of catastrophic variables: classic nova, dwarf nova, multiple supernova, and others. All types share the same basic mechanics. A pair of stars orbit each other closely, and one star is larger than the other. The more massive ones are called primary stars, and draw gas from lower-mass stars, which astronomers call donor stars.

The main star in the CV is a white dwarf, and the donor star is usually a red dwarf. Red dwarfs are cooler and less massive than white dwarfs. They have a mass between 0.07 and 0.30 solar masses and a radius of about 20 percent that of the Sun. A primary white dwarf star has a typical mass of about 0.75 solar masses but a much smaller radius, about the same as Earth’s.

When the main star pulls material from the donor star, the material forms an accretion disk around the primary star. The material in the accretion disk heats up, and it causes an increase in luminosity. The increase can beat the light from a pair of stars.

If there is a faint third object – a planet – in the system, then its gravity could affect the transfer of matter from the donor to the main star. This interference affects the brightness of the system, and that’s what the new study is all about.

The study’s authors show how the chaotic environment around CV can host planets and explain how astronomers were able to find them. This research is “Test the third object hypothesis in disaster variables LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis.” It was published in Monthly Notices of the Royal Astronomical Society (MNRA). The lead author is Dr. Carlos Chavez, from the Universidad Autonoma De Nuevo León in Mexico.

Matter drawn to the main star gathers in the accretion ring and heats up, creating increased luminosity. But material transfer to disk is unstable; it rises and falls as the stars in the CV orbit each other. Chavez and his colleagues examined four disaster variables in their study: LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis.

The four CVs exhibit a very long photometric period (VLPP), which is a period of increasing luminosity that does not correspond to the period of the binary orbit.

There is a point between the two stars and a third object called the L1 point, or the Lagrangian point. This is the point of gravitational balance between the stars. The L1 point is dynamic, and its position changes as the star moves. Lead author Chavez pointed out in an earlier paper that a third body, a planet, could cause oscillations at point L1.

As the L1 point changes, the amount of matter being attracted to the main star – the rate of mass transfer – changes. A change in the mass transfer rate creates a change in the luminosity of the entire three-body system.

By measuring a change in brightness of four CVs, the researchers calculated the distance and mass of a potential third object in the system based on the change in brightness in each system.

Their calculations show that the variation has a much longer period than the orbital period of the stars. According to the team, two of the four CVs they studied had “planetary-like objects” orbiting them.

“Our work has proven that a third object can interfere with catastrophic variables in such a way that it can cause changes in brightness in the system,” Chavez said in a press release. “This perturbation could explain the very long observed period – between 42 and 265 days – and the amplitude of the change in brightness. Of the four systems we studied, our observations showed that two out of four had objects of planetary mass in orbit around them. “

This isn’t the first time scientists have tackled CVs and tried to find an explanation for variations in luminosity.

In 2017 a separate research team published a paper presenting their four CVs and VLPPs. They suggested that planets were the cause. But they say that “…the orbital plane of the third body must be greater than 39.2 degrees for this mechanism to effectively disrupt the inner binary.”

“Here we explore a new possibility, namely that secular perturbation by low eccentricity and a third low-sloping object explains VLPP as well as the observed magnitude changes in these four CVs,” write Chavez and co-authors in their paper. They say that “…a third object in a near-circular planar orbit can produce perturbations in the central binary eccentricity.”

According to Chavez, their work represents a new way to detect exoplanets. Planet hunters find most exoplanets using transit systems. When an exoplanet transits in front of its star, there is a detectable drop in the star’s light.

While effective – we have discovered thousands of planets this way – the transit method has its limitations. It only works when everything is lined up correctly. We have to look at it from the side, otherwise the planet doesn’t transit the star from our point of view, and there’s no starlight drop.

But the method that Chavez and his colleagues developed does not rely on planetary transits. It relies on an intrinsic change in luminosity which can be observed from different angles.

This article was originally published by Universe Today. Read the original article.

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