Secondary star in omicron Ceti (Mira B) might be a very low mass white dwarf

Star system: Omicron Ceti A | Distance from the Sun: 299 light years

Mira, also known as omicron Ceti, is one of the most famous variable stars known since antiquity — a giant red star located about 300 light-years away that brightens and dims over a cycle of roughly 332 days. It is not alone: Mira has a faint companion called Mira B, thought to be a white dwarf, the dense Earth-sized remnant left behind when a Sun-like star exhausts its nuclear fuel. A new study used observations of rapid brightness flickering in the Mira system to measure the mass and properties of Mira B.
Astronomers observed Mira on 7 nights between August and October 2025, timing the campaign to coincide with the minimum brightness phase of Mira's pulsation cycle. They recorded rapid, small-scale brightness variations — known as flickering — in two standard wavelength bands called Johnson B and V. Flickering in such systems is caused by gas falling from one star onto the other through an accretion disc, a rotating ring of material that surrounds the white dwarf. The measured peak-to-peak flickering amplitude ranged from 0.11 to 0.28 magnitudes in the B band, corresponding to a luminosity of the flickering source between 0.10 and 0.46 solar luminosities.
The material feeding the disc is thought to arrive through a mechanism called Wind Roche Lobe Overflow (WRLOF): Mira continuously sheds gas in a stellar wind, and part of that wind is captured by the gravitational pull of Mira B. Using the observed flickering amplitude and its established relationship to disc brightness, the team calculated an average accretion disc luminosity of 0.91 ± 0.28 solar luminosities.
Key findings
Mira B is a low-mass white dwarf with a mass of 0.24 ± 0.04 solar masses, placing it in the rare category of extremely low-mass white dwarfs
The average luminosity of its accretion disc is estimated at 0.91 ± 0.28 solar luminosities
Mira B accretes mass at a rate of approximately 6.8 × 10⁻⁹ solar masses per year
The mass transfer mechanism is consistent with Wind Roche Lobe Overflow (WRLOF)

Scientific study

Is Mira B a low mass white dwarf? (external link)