The exceptionally sparse gas of the Local Bubble is the result ofsupernovae that exploded within the past ten to twenty million years.Geminga, apulsar in theconstellation Gemini, was once thought to be the remnant of a single supernova that created the Local Bubble, but now multiple supernovae in subgroup B1 of thePleiadesmoving group are thought to have been responsible,[5] becoming a remnantsupershell.[6] Other research suggests that the subgroups Lower Centaurus–Crux (LCC) and Upper Centaurus–Lupus (UCL), of theScorpius–Centaurus association created both the Local Bubble and the Loop I Bubble, with LCC being responsible for the Local Bubble and UCL being responsible for the Loop I Bubble.[7] It was found that 14 to 20 supernovae originated from LCC and UCL, which could have formed these bubbles.[8]
TheSolar System has been traveling through the region currently occupied by the Local Bubble for the last five to ten million years.[9] Its current location lies in theLocal Interstellar Cloud (LIC), a minor region of denser material within the Bubble. The LIC formed where the Local Bubble and theLoop I Bubble met. The gas within the LIC has a density of approximately 0.3 atoms per cubic centimeter.
The Local Bubble is not spherical, but appears to be narrower in thegalactic plane, becoming somewhat egg-shaped or elliptical, and may widen above and below the galactic plane, becoming shaped like an hourglass. It abuts other bubbles of less dense interstellar medium (ISM), including, in particular, the Loop I Bubble. The Loop I Bubble was cleared, heated, and maintained by supernovae andstellar winds in theScorpius–Centaurus association, some 500 light years from theSun. The Loop I Bubble contains the starAntares (also known as α Sco, or Alpha Scorpii), as shown on the diagram above right. Several tunnels connect the cavities of the Local Bubble with the Loop I Bubble, called the "Lupus Tunnel".[10] Other bubbles adjacent to the Local Bubble are theLoop II Bubble and theLoop III Bubble. In 2019, researchers found interstellar iron in Antarctica which they relate to theLocal Interstellar Cloud, which might be related to the formation of the Local Bubble.[11]
Local stars in the galactic plane (click for rotation)
Launched in February 2003 and active until April 2008, a small space observatory calledCosmic Hot Interstellar Plasma Spectrometer (CHIPSat) examined the hot gas within the Local Bubble.[12] The Local Bubble was also the region of interest for theExtreme Ultraviolet Explorer mission (1992–2001), which examined hot EUV sources within the bubble. Sources beyond the edge of the bubble were identified but attenuated by the denser interstellar medium. In 2019, the first 3D map of the Local Bubble was reported using observations of diffuse interstellar bands.[13]In 2020, the shape of the dusty envelope surrounding the Local Bubble was retrieved and modeled from 3D maps of the dust density obtained from stellar extinction data.[14]
As the bubble expands it sweeps interstellar gas and dust which collapse to form new stars on its surface but not inside. The Sun entered the bubble around five million years ago.[15][16]Local Bubble and itsmolecular clouds
In January 2022, a paper in the journalNature found that observations and modeling had determined that the action of the expanding surface of the bubble had collected gas and debris and was responsible for the formation of all young, nearby stars.[17]
Severalradioactive isotopess onEarth have been connected to supernovae occurring relatively nearby to the solar system. The most common source is found in deep seaferromanganese crustss, which are constantly growing and deposit iron, manganese, and other elements. Samples are divided into layers which are dated, for example, withBeryllium-10. Some of these layers have higher concentrations of radioactive isotopes.[18] The isotope most commonly associated with supernovae on Earth isIron-60 fromdeep sea sediments,[19]Antarctic snow,[20] andlunar soil.[21] Other isotopes areManganese-53[22] andPlutonium-244[18] from deep sea materials. Supernova-originatedAluminium-26, which was expected from cosmic ray studies, was not confirmed.[23] Iron-60 and Manganese-53 have a peak 1.7–3.2 million years ago, and Iron-60 has a second peak 6.5–8.7 million years ago. The older peak likely originated when the solar system moved through theOrion–Eridanus Superbubble and the younger peak was generated when the solar system entered the Local Bubble 4.5 million years ago.[24] One of the supernovae creating the younger peak might have created the pulsarPSR B1706-16 and turnedZeta Ophiuchi into arunaway star. Both originated from UCL and were released by a supernova 1.78 ± 0.21 million years ago.[25] Another explanation for the older peak is that it was produced by one supernova in theTucana-Horologium association 7-9 million years ago.[26]
^Abt, Helmut A. (December 2015). "Hot gaseous stellar disks avoid regions of low interstellar densities".Publications of the Astronomical Society of the Pacific.127 (958):1218–1225.Bibcode:2015PASP..127.1218A.doi:10.1086/684436.S2CID124774683.
^"Our local galactic neighborhood".Interstellar.jpl.nasa.gov. National Aeronautics and Space Administration (NASA). 8 February 2000. Archived fromthe original on 21 November 2013. Retrieved23 July 2013.
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