A Blue large-amplitude pulsator (BLAP) is a proposed class of

pulsating variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

. They are extremely rare, with only 14 being known after examining around a billion stars from the

Optical Gravitational Lensing Experiment The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable ...

(OGLE) survey.

Discovery

Blue large-amplitude pulsators were discovered by a team of astronomers from the

University of Warsaw The University of Warsaw ( pl, Uniwersytet Warszawski, la, Universitas Varsoviensis) is a public university in Warsaw, Poland. Established in 1816, it is the largest institution of higher learning in the country offering 37 different fields o ...

and announced in ''Nature Astronomy'' journal in June 2017. During a 2013 search for

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

s with periods shorter than one hour, a star with a period of 28.26 minutes was detected and tentatively classified as a

δ Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a subclass of young pulsating star. These variables as well as classical cepheids are important standard candles and have been used to es ...

although it had an unusually large amplitude and short period. Examination of over one billion

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

stars made during the OGLE project revealed another 13 objects with similar properties: periods of 22 - 39 minutes;

near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

amplitudes of 0.19 - 0.36 magnitudes; extremely blue, suggesting temperatures around 30,000 K; and smaller than main sequence stars of that temperature.

Characteristics

Stars of this type are characterized by changes of several dozen percent of the brightness on an average of half an hour (between 20-40 minutes). A detailed analysis of the observation results confirms that BLAP objects have a temperature of about 30,000 °C, and the cause for the changes in brightness is pulsation. The construction model is similar to giant star models - 96% of the mass is concentrated in a

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

of only 20% of the radius of the entire star. The rest of the mass is a slightly ruffled envelope that pulsates at rapid rhythm - hence the large amplitude of the glare. Currently, the theory only explains how BLAP stars are built and how their brightness changes, while there are only hypotheses about the formation of such stars. One of the hypotheses is that these stars must have lost a large portion of their mass at some point in their

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

to be as hot as they are now. Scientists assume that such a configuration can not come through the evolution of a lonely star, and one possibility is, for example, the passage of a star in the vicinity of a supermassive black hole to the center of the galaxy. Then the black hole can deprive the star of the outer layer; but as the scientists suggest, such a scenario is very unlikely. Another more likely hypothesis assumes that these objects can be formed after the merger of two small mass stars.

References

{{Variable star topics Variable stars