Showing posts with label distant star cluster. Show all posts
Showing posts with label distant star cluster. Show all posts

Monday, August 14, 2023

Webb Reveals Colors of Earendel, Most Distant Star Ever Detected

Sunrise Arc (NIRCam Image)
Credits: Image: NASA, ESA, CSA
Science: Dan Coe (STScI/AURA for ESA, JHU), Brian Welch (NASA-GSFC, UMD)
Image Processing: Zolt G. Levay


Sunrise Arc Zoom-In (NIRCam Image)
Credits: Image: NASA, ESA, CSA
Science: Dan Coe (STScI/AURA for ESA, JHU), Brian Welch (NASA-GSFC, UMD)
Image Processing: Zolt G. Levay




NASA’s James Webb Space Telescope has followed up on observations by the Hubble Space Telescope of the farthest star ever detected in the very distant universe, within the first billion years after the big bang. Webb’s NIRCam (Near-Infrared Camera) instrument reveals the star to be a massive B-type star more than twice as hot as our Sun, and about a million times more luminous.

The star, which the research team has dubbed Earendel, is located in the Sunrise Arc galaxy and is detectable only due to the combined power of human technology and nature via an effect called gravitational lensing. Both Hubble and Webb were able to detect Earendel due to its lucky alignment behind a wrinkle in space-time created by the massive galaxy cluster WHL0137-08. The galaxy cluster, located between us and Earendel, is so massive that it warps the fabric of space itself, which produces a magnifying effect, allowing astronomers to look through the cluster like a magnifying glass.

While other features in the galaxy appear multiple times due to the gravitational lensing, Earendel only appears as a single point of light even in Webb’s high-resolution infrared imaging. Based on this, astronomers determine the object is magnified by a factor of at least 4,000, and thus is extremely small – the most distant star ever detected, observed 1 billion years after the big bang. The previous record-holder for the most distant star was detected by Hubble and observed around 4 billion years after the big bang. Another research team using Webb recently identified a gravitationally lensed star they nicknamed Quyllur, a red giant star observed 3 billion years after the big bang.

Stars as massive as Earendel often have companions . Astronomers did not expect Webb to reveal any companions of Earendel since they would be so close together and indistinguishable on the sky. However, based solely on the colors of Earendel, astronomers think they see hints of a cooler, redder companion star. This light has been stretched by the expansion of the universe to wavelengths longer than Hubble’s instruments can detect, and so was only detectable with Webb.

Webb’s NIRCam also shows other notable details in the Sunrise Arc, which is the most highly magnified galaxy yet detected in the universe’s first billion years. Features include both young star-forming regions and older established star clusters as small as 10 light-years across. On either side of the wrinkle of maximum magnification, which runs right through Earendel, these features are mirrored by the distortion of the gravitational lens. The region forming stars appears elongated, and is estimated to be less than 5 million years old. Smaller dots on either side of Earendel are two images of one older, more established star cluster, estimated to be at least 10 million years old. Astronomers determined this star cluster is gravitationally bound and likely to persist until the present day. This shows us how the globular clusters in our own Milky Way might have looked when they formed 13 billion years ago.

Astronomers are currently analyzing data from Webb’s NIRSpec (Near-Infrared Spectrograph) instrument observations of the Sunrise Arc galaxy and Earendel, which will provide precise composition and distance measurements for the galaxy.

Since Hubble’s discovery of Earendel, Webb has detected other very distant stars using this technique, though none quite as far as Earendel. The discoveries have opened a new realm of the universe to stellar physics, and new subject matter to scientists studying the early universe, where once galaxies were the smallest detectable cosmic objects. The research team has cautious hope that this could be a step toward the eventual detection of one of the very first generation of stars, composed only of the raw ingredients of the universe created in the big bang – hydrogen and helium.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.




About This Release

Credits:

Media Contact:

Leah Ramsay
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Dan Coe (STScI/AURA for ESA, JHU), Brian Welch (NASA-GSFC, UMD)

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Contact Us: Direct inquiries to the News Team.

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Tuesday, May 16, 2017

Gemini Tracks Distant Star Cluster with Adaptive Optics

Figure 1: Gemini Multi-Object Spectrograph (GMOS-South) of the Pyxis field (left image), with the center of the cluster marked with a red star. A zoom of the pseudo color image of Pyxis observed with the Gemini South Adaptive Optics Imager (GSAOI) used with the Gemini Multi-conjugate adaptive optics System (GeMS) is shown at right. The field of view of GMOS is 5 x 5 arcminutes, 85 x 85 arcseconds for GeMS.

Figure 2: Absolute velocity of Pyxis. Each blue dot stands for a velocity derived from a single background galaxy. The red box shows the weighted average velocity derived from all galaxies. Only galaxies with small errors are shown for clarity.


Researchers combine images from Gemini South’s wide-field adaptive optics system (GeMS/GSAOI) with data from the Hubble Space Telescope (HST) to determine the proper motion of a distant cluster of stars. The observations, the first to use ground-based adaptive optics to precisely measure the motion of a cluster at such a large distance, allowed astronomers to set a lower limit for the mass of our Milky Way while providing clues about the cluster’s origin. 
 
A study of the proper motion (apparent motion in the sky due to an object's motion around our galaxy) of several substructures across the Milky Way’s halo is underway at Gemini South. As part of this study the team used Adaptive Optics (AO) at Gemini South, along with data from HST, to focus on a distant cluster called Pyxis. The work allowed the team to set a lower limit for the Milky Way’s mass of 950 million solar masses. This value is consistent with most, but not all, previous determinations.

The wide-field Gemini Multi-conjugate adaptive optics System (GeMS) combined with the Gemini South Adaptive Optics Imager (GSAOI) provided the Gemini data. “We used GeMS/GSAOI to estimate the proper motion for halo objects because normal (seeing limited) ground-based telescopes need a time baseline of more than 15 years for this measurement,” says Tobias Fritz (University of Virginia) who leads the research team. “GeMS/GSAOI with its better spatial resolution can make that measurement in five years, the same types of baselines required from space-based proper motions (like HST),” continues Fritz. The team was able to measure absolute proper motions of Pyxis using GeMS/GSAOI, which provided a resolution of 0.08 arcsecond and combined that with archival HST images, with a resolution of ~ 0.1 arcsecond. Fritz adds, “The study of motions for halo objects, like Pyxis, can constrain the mass distribution of our Galaxy at large distances and thus the mass of the Milky Way.”

Pyxis, a densely packed collection of ancient stars, is one of the most distant examples of a globular clusters, dense clusters of stars which orbit our galaxy. The cluster is located some 130,000 light years away and is thought to be about 2 billion years younger than other globular clusters with the same ratio of heavier elements (metallicity). Together, these characteristics imply Pyxis did not form with other Milky Way clusters. Instead, it is likely that Pyxis was formed in a massive dwarf galaxy that was then accreted by the Milky Way. Thus, Pyxis has an extragalactic origin. However, the orbits of the known massive dwarf galaxies are inconsistent with the orbit of Pyxis, which is derived from the new proper motion measurements.

The paper, titled: The Proper Motion of Pyxis: The First Use of Adaptive Optics in Tandem with HST on a Faint Halo Object is published in The Astrophysical Journal. The work is part of a Large and Long program at Gemini that is also targeting other clusters, dwarf galaxies, and individual stars in stellar streams.

Abstract

We present a proper motion measurement for the halo globular cluster Pyxis, using HST/ACS data as the first epoch, and GeMS/GSAOI Adaptive Optics data as the second, separated by a baseline of ∼ 5 years. This is both the first measurement of the proper motion of Pyxis and the first calibration and use of Multi-Conjugate Adaptive Optics data to measure an absolute proper motion for a faint, distant halo object. Consequently, we present our analysis of the Adaptive Optics data in detail. We obtain a proper motion of µα cos(δ) =1.09±0.31 mas yr−1 and µδ =0.68±0.29 mas yr−1. From the proper motion and the line-of-sight velocity we find the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. We also investigate two literature-proposed associations for Pyxis with the recently discovered ATLAS stream and the Magellanic system. Combining our measurements with dynamical modeling and cosmological numerical simulations we find it unlikely Pyxis is associated with either system. We examine other Milky Way satellites for possible association using the orbit, eccentricity, metallicity, and age as constraints and find no likely matches in satellites down to the mass of Leo II. We propose that Pyxis probably originated in an unknown galaxy, which today is fully disrupted. Assuming that Pyxis is bound and not on a first approach, we derive a 68% lower limit on the mass of the Milky Way of 0.95×1012 M⊙.