Earendel: The Distant Beacon

WHL0137-LS, more commonly known as Earendel, is a celestial entity—either a single star or a compact star cluster—situated within the constellation Cetus.

🌌 Overview and Discovery

First identified in 2022 via the Hubble Space Telescope (HST), Earendel holds a prestigious place in astronomy. With a comoving distance of approximately $28 \times 10^9$ light-years (roughly $8.6 \text{ Gpc}$), it is currently the most distant individual star ever detected if it is indeed a single object.

Prior to this discovery, the record was held by Icarus (MACS J1149 Lensed Star 1), which sits at a comoving distance of $14.4 \times 10^9$ light-years. However, recent data from the James Webb Space Telescope (JWST) suggests that Earendel may actually be a star cluster rather than a solitary star.

The Mechanism of Visibility

The detection of such a distant object is only possible through gravitational lensing. This occurs when a massive foreground object warps spacetime, acting as a natural magnifying glass.

"Objects like Earendel can be observed at cosmological distances thanks to the large magnification factors afforded by gravitational lensing, which can exceed 1,000."

🔭 Observation History

The discovery process involved multiple exposures and instruments:

• Hubble Exposure Dates:
  • June 7, 2016
  • July 17, 2016
  • November 4, 2019
  • November 27, 2019
• JWST Milestones:
  • July 30, 2022: First imaging campaign.
  • August 8, 2023: Color detection and combined Hubble/Webb imagery.

Research Objectives

The scientific community has set several goals for ongoing study:

• Capture initial images via HST.
• Determine basic color and luminosity via JWST.
• Perform full spectral analysis to identify elements heavier than $\text{H}$ and $\text{He}$.
• Confirm if the object is a single star or a cluster.

🛠 Technical Specifications

The nature of Earendel remains a subject of debate. Below are the estimated parameters based on different models:

Additional Data:

• Spectral Type: B
• Apparent Magnitude (F435W): $27.2$
• Variable Type: Luminous blue variable

🏷 Etymology and Nomenclature

The name Earendel was chosen by the discovery team for its poetic and literary roots:

1. Old English: It translates to "morning star" or "rising light".
2. Literature: It is a nod to J.R.R. Tolkien's The Silmarillion, featuring the half-elven character Eärendil who sails the sky with a brilliant jewel.

The host galaxy, WHL0137-zD1, is referred to as the "Sunrise Arc" due to the crescent shape created by the gravitational lens.

📉 Recent Findings and Controversies

While initial simulations suggested a magnification factor between $1,000\times$ and $40,000\times$, newer research has challenged this. A 2025 study provides a much lower estimate for the magnification: $\mu = 43\text{--}67$

Furthermore, JWST's NIRCam data identifies Earendel as a massive B-type star that is:

• $\text{Temperature} > 2 \times \text{Sun}$
• $\text{Luminosity} \approx 1,000,000 \times \text{Sun}$

There are also indications of a companion star that is redder and cooler. Other similar candidates, such as "Godzilla," have been spotted, though their classifications remain contested.

Coordinate Data

{
  "object": "Earendel",
  "coordinates": {
    "RA": "01h 37m 23.232s",
    "Dec": "-08° 27′ 52.20″",
    "Epoch": "J2000",
    "Constellation": "Cetus"
  }
}

Figure 1: Representation of the galaxy cluster WHL0137-08 and the position of Earendel.