Hubble captures a 'blue lurker' multi-star system

Despite how it may sound, a blue lurker is not a villainous character from a comic book. It is a rare type of star, adrift in the vast cosmic ocean.

This intriguing star, studied by the Hubble Space Telescope, lies in the depths of the open star cluster known as M67, about 2,800 light-years from Earth.

Its unusual name hints at the mysterious and complex story behind its discovery and behavior, that make it a standout among celestial phenomena.

Mysterious triple star system

This star has had a dramatic life involving gravity, dust, light, and spin that have interacted over millions of years.

It is thought to be part of an unusual three-star system where the other two stars merged and left their impact on the remaining lurker by making it spin faster than predicted.

The star’s accelerated rotation makes it stand out, although in terms of its appearance, it blends in well with the other Sun-like stars in the cluster.

The fact that it looks like other stars but is different in terms of spin rate has earned it the title of “lurker.”

Blue lurker: A quickspin star

A closer look at the lurker’s high spin rate reveals that the star has likely accreted material from a companion star, which has caused a spike in its spin cycle.

Unlike usual Sun-like stars that complete one rotation in approximately 30 days, the blue lurker pulls it off in just four days.

This discovery was made by NASA’s retired Kepler Space Telescope, and highlights the incredible capacities that our space-exploration instruments are capable of.

Fascinating tale of the blue lurker

Emily Leiner from the Illinois Institute of Technology in Chicago calls the journey of the blue lurker a “super complicated evolutionary story.”

Starting its cosmic life at a more leisurely pace, the blue lurker initially orbited a binary system made up of two, Sun-like stars.

Approximately 500 million years ago, the two stars in the binary system merged, forming a more massive star.

This newly created giant went on to share some of its material with the blue lurker, which caused it to rotate more rapidly.

Fast forward till today, and we find the blue lurker in the company of a white dwarf star – a vestige of the once massive merger.

The importance of multi-star systems

Multi-star systems, although constituting only 10% of the Sun-like star population, are very significant because they often end up with intriguing celestial outcomes.

However, a comprehensive model that connects all stages of their evolution is yet to be established.

Despite this, our observations allow us to piece together the story of triple-star systems, especially when accompanied by spectral data.

The white dwarf companion

Hubble’s ultraviolet spectroscopy observation of the white dwarf companion to the blue lurker revealed that the dwarf is incredibly hot with temperatures reaching up to 23,000 degrees Fahrenheit, which is about three times the Sun’s surface temperature.

The white dwarf and possesses a hefty 0.72 solar masses.

Theoretically, hot white dwarfs in M67 should be about 0.5 solar masses in size, but the white dwarf companion to the lurker weighs in at a hefty 0.72 solar masses.

This suggests that the observed white dwarf is a remnant of the merger of the two stars in the triple-star system.

Blue Lurker and the celestial chronicle

Triple-star systems are beginning to feature more prominently in the cosmic narrative because of their explosive end products.

“Triples are emerging as potentially very important to creating interesting, explosive end products. It’s really unusual to be able to put constraints on such a system as we are exploring,” said Leiner.

“This is one of the only triple systems where we can tell a story this detailed about how it evolved,” she added.

She presented these fascinating findings at the 245th meeting of the American Astronomical Society in Washington, D.C.

Hubble: An instrument of grand discoveries

Hubble, an international project between NASA and the European Space Agency (ESA), has been operational for over three decades.

It has made breakthrough discoveries that have reshaped our understanding of the universe.

Notably, NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations, with support from Lockheed Martin Space, Denver.

The Space Telescope Science Institute in Baltimore, run by the Association of Universities for Research in Astronomy, carries out Hubble’s science operations for NASA.

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