Godzilla (star)

{{Short description|Star in the Sunburst galaxy}}

{{Other uses|Godzilla (disambiguation)}}

{{Starbox begin}}

{{Starbox image

|image= {{CSS image crop

|Image = 3000px

|bSize = 3000

|cWidth = 300

|cHeight = 300

|oTop = 800

|oLeft = 1672

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| caption = The transient candidate dubbed Godzilla is the bright spot at the very center, at the left edge of the arc and immediately above the orange, foreground star. Cropped from original image.

| credit = ESA/Hubble, NASA, Rivera-Thorsen et al.

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{{Starbox observe

| epoch=J2000.0

| ra={{RA|15|50|00.66}}

| dec={{DEC|-78|11|10.0}}

| constell=Apus

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{{Starbox character

| type=LBV?

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{{Starbox astrometry

| absmag_v=−17.3{{snd}}−14.8,{{efn|name=absmag1}} <−14.7{{efn|name=absmag2}}

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{{Starbox detail

| radius=430{{snd}}2,365

| temperature=15,000{{snd}}30,000

| luminosity=134,000,000{{snd}}255,000,000{{efn|name=luminosity}}

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{{Starbox catalog

| names=Godzilla star

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Godzilla is a variable star in the Sunburst galaxy at redshift z = 2.37 (or 10.9 billion light years from Earth), observed through the gravitational lens PSZ1 G311.65-18.48. It was originally identified in the NW arc as a possible transient event in images taken with the Hubble Space Telescope (HST).

As of October 2022, it is the most luminous star that can be currently observed. This is possible because the star is believed to be undergoing an episode of temporary increased luminosity that has lasted at least seven years, combined with an estimated magnification of at least a factor of 2000.

Some spectral features in Godzilla resemble those of other variable stars in the Milky Way Galaxy such as Eta Carinae, suggesting that Godzilla could be close to the end of its life. Godzilla is believed to be going through an episode similar to the Great Eruption of Eta Carinae in the 19th century, during which the star was likely among the brightest in the universe at about {{solar luminosity|50 million}}.

The extreme magnification of Godzilla is partially due to a nearby substructure, probably a dwarf galaxy, not seen in the HST images (but recently detected in new JWST images), that is also close to the critical curve of the cluster. This unobserved substructure is believed to be dominated by dark matter.

Godzilla is named after the Kaiju and makes reference to its monstrous nature. Other stars named after Kaiju include Mothra, which shares many of the characteristics of Godzilla.

A 2024 paper showed that Godzilla's source-frame ultraviolet light and nebular emission lines as measured by MUSE and X-shooter at the Very Large Telescope (VLT) can be quantitatively explained as that of a star cluster 4-6 Myr after formation and weighing millions of solar masses, magnified by a factor between about 500 and 2000. The authors show that the ionized gas as the source of Godzilla's nebular emission is enriched with nitrogen and possibly oxygen and helium too, and suggest that the gas is stellar wind and supernova ejecta condensed in the gravitational potential of the star cluster and is excited by ionizing stellar radiation. Based on the non-detection of flux time variability, which should be induced by intracluster microlensing effects but would be diluted if the source consists of many stars, the study suggests that Godzilla's magnification factor is lower than previously thought, in the range of hundreds. This casts doubt on the hypothesis that Godzilla's light is dominated by one or a few highly magnified stars.