zoe hackshaw
@theastrozo.bsky.social
space cowgirl (UTAustin Astronomy Ph.D. candidate) & investigator of Galactic origins🔎💫🔭🧘♀️🤠🪩 UF alum🫶🏼 zoehackshaw.github.io
We find no chemical peculiarities in BH3*.
The chemical "normalcy” of this star is consistent with both formation theories for Gaia BH3, including dynamical capture and isolated binary evolution.
Many more systems of this kind are anticipated to be discovered with the coming release of Gaia DR4!
The chemical "normalcy” of this star is consistent with both formation theories for Gaia BH3, including dynamical capture and isolated binary evolution.
Many more systems of this kind are anticipated to be discovered with the coming release of Gaia DR4!
December 16, 2025 at 7:38 PM
We find no chemical peculiarities in BH3*.
The chemical "normalcy” of this star is consistent with both formation theories for Gaia BH3, including dynamical capture and isolated binary evolution.
Many more systems of this kind are anticipated to be discovered with the coming release of Gaia DR4!
The chemical "normalcy” of this star is consistent with both formation theories for Gaia BH3, including dynamical capture and isolated binary evolution.
Many more systems of this kind are anticipated to be discovered with the coming release of Gaia DR4!
Some heavy elements decay on cosmological timescales. We use our upper limit on Th and Eu detection to try to age this star.
We get an age of 22.8 billion years. Considering the universe is about 13.6 billion yr old, this is pretty unlikely!
Sources for error include model assumptions (see paper)
We get an age of 22.8 billion years. Considering the universe is about 13.6 billion yr old, this is pretty unlikely!
Sources for error include model assumptions (see paper)
![We show the observed spectrum of BH3* in black points with a synthetic spectrum fit to [Th/Fe] = 0.25 (pink) and a ±0.1 dex region around our fit (purple). A Th abundance of [Th/Fe]= −∞ is shown with the blue dashed line. We then fix an age of 13.4 Gyr (found with isochrones) and the H. Schatz et al. (2002) production ratio to solve for the [Th/Fe] needed, resulting in [Th/Fe] = 1.14 (green). We show that the Th abundance found using the probable age and production ratio cannot conceivably fit our observed data.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zsvhvmyp7vx3kt27tk56adyy/bafkreie2wrmmnsapiftxldrq6cfnqxxidhdolsewxyn3iqyp7nwdkwsyc4@jpeg)
December 16, 2025 at 7:35 PM
Some heavy elements decay on cosmological timescales. We use our upper limit on Th and Eu detection to try to age this star.
We get an age of 22.8 billion years. Considering the universe is about 13.6 billion yr old, this is pretty unlikely!
Sources for error include model assumptions (see paper)
We get an age of 22.8 billion years. Considering the universe is about 13.6 billion yr old, this is pretty unlikely!
Sources for error include model assumptions (see paper)
It's pretty rare to encounter r-proc elements in metal-poor stars - only ~15% of halo stars are r-rpoc enhanced!
There is only 1 ED-2 star with an Eu abundance, but no chemical peculiarities there either.
Now for the last bit of this project: nuclear cosmo chronometry
There is only 1 ED-2 star with an Eu abundance, but no chemical peculiarities there either.
Now for the last bit of this project: nuclear cosmo chronometry
December 16, 2025 at 7:31 PM
It's pretty rare to encounter r-proc elements in metal-poor stars - only ~15% of halo stars are r-rpoc enhanced!
There is only 1 ED-2 star with an Eu abundance, but no chemical peculiarities there either.
Now for the last bit of this project: nuclear cosmo chronometry
There is only 1 ED-2 star with an Eu abundance, but no chemical peculiarities there either.
Now for the last bit of this project: nuclear cosmo chronometry
Now for the REALLY weird stuff, the heaviest elements. We try to derive rapid-neutron capture element abundances (r-proc), and we find that this star is mildly r-proc enhanced!
You can tell by the Eu abundance of [Eu/Fe] = 0.57. We report an upper limit for Th of [Th/Fe] < 0.25 but ... no Uranium😕
You can tell by the Eu abundance of [Eu/Fe] = 0.57. We report an upper limit for Th of [Th/Fe] < 0.25 but ... no Uranium😕
![Left: The observed spectrum of BH3* in black points, with a synthetic spectrum fit to an Eu abundance of [Eu/Fe] = 0.57 in pink and a ±0.1 dex region around this abundance (purple). Middle: The observed spectrum of the red giant in Gaia BH3 in black points, with a synthetic spectrum fit to a Th abundance of [Th/Fe] = 0.25 in pink and a ±0.1 dex region around this abundance (purple). This highlights the possibility of a Th detection at this line. Right: Observed spectrum (black points) compared to a synthesized spectrum with [U/Fe] ∼ −∞ (pink). Gray curves show synthetic spectra from [U/Fe] = −0.75 to 1.75 in 0.1 dex steps in
the top panel, and the range of differences from the observed spectrum and synthetic spectra are shown in green in the bottom panel. No uranium feature is clearly detected. The nearby Fe I line at 3859.91 Å appears saturated, complicating the measurement of the U II 3859 Å line.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zsvhvmyp7vx3kt27tk56adyy/bafkreia4gzwgv65lrbwclcjghjoqztasp4hf4denwk7iad2hejyevhjyui@jpeg)
December 16, 2025 at 7:29 PM
Now for the REALLY weird stuff, the heaviest elements. We try to derive rapid-neutron capture element abundances (r-proc), and we find that this star is mildly r-proc enhanced!
You can tell by the Eu abundance of [Eu/Fe] = 0.57. We report an upper limit for Th of [Th/Fe] < 0.25 but ... no Uranium😕
You can tell by the Eu abundance of [Eu/Fe] = 0.57. We report an upper limit for Th of [Th/Fe] < 0.25 but ... no Uranium😕
We repeat this for all of the elements we derived.
In all panels, we are looking to see how well the chemical abundances of Gaia BH3* (pink star) agree with other ED-2 stars (Dodd et al. 2025; pink squares).
No peculiarities so far in the light, alpha, Fe-peak or light n-cap elements!
In all panels, we are looking to see how well the chemical abundances of Gaia BH3* (pink star) agree with other ED-2 stars (Dodd et al. 2025; pink squares).
No peculiarities so far in the light, alpha, Fe-peak or light n-cap elements!
December 16, 2025 at 7:25 PM
We repeat this for all of the elements we derived.
In all panels, we are looking to see how well the chemical abundances of Gaia BH3* (pink star) agree with other ED-2 stars (Dodd et al. 2025; pink squares).
No peculiarities so far in the light, alpha, Fe-peak or light n-cap elements!
In all panels, we are looking to see how well the chemical abundances of Gaia BH3* (pink star) agree with other ED-2 stars (Dodd et al. 2025; pink squares).
No peculiarities so far in the light, alpha, Fe-peak or light n-cap elements!
We plot the abundances of Gaia BH3* to ask the question, how similar does it look to its neighbors?
Gaia BH3 is in a halo stream called ED-2. We know that stars that are born together should look similar, so are there any chemical peculiarities in Gaia BH3*?
Looking at the light elements, no!
Gaia BH3 is in a halo stream called ED-2. We know that stars that are born together should look similar, so are there any chemical peculiarities in Gaia BH3*?
Looking at the light elements, no!
![Figure 3. A multipanel plot showing the Li (left), C (middle), and Na (right) abundances of BH3* (pink star) compared to the dSph Sculptor (blue triangles; D. Geisler et al. 2005), the UFD Reticulum II (upside-down purple triangles; A. P. Ji et al. 2016), BH3*’s host halo stream ED-2 (pink squares; E. Dodd et al. 2025), the GC M15 (green crosses; J. S. Sobeck et al. 2011), and other MW halo stars (gray circles; I. U. Roederer et al. 2014b). In all of the panels, [X/Fe] is on the y-axis, with the exception of the first panel which shows lithium in terms of absolute abundance. The dashed line at 0 represents the solar abundance of [X/Fe]. The left
panel shows the Spite plateau annotated in purple, illustrating that BH3* lies well below the Spite plateau at A(Li) ∼ 2.2 dex (F. Spite & M. Spite 1982). We separate dwarf stars (triangles) and giant stars (squares) in the left panel to show that metal-poor dwarf stars make up the Spite plateau and giant stars have largely undergone the burning of their lithium.
So far, the abundances of Gaia BH3* seem to align with other ED-2 stars!](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:zsvhvmyp7vx3kt27tk56adyy/bafkreiarq56w6kxl7rtn2ybsb6ih54nko6soxbtsoshc3jd6qsioyiqxja@jpeg)
December 16, 2025 at 7:23 PM
We plot the abundances of Gaia BH3* to ask the question, how similar does it look to its neighbors?
Gaia BH3 is in a halo stream called ED-2. We know that stars that are born together should look similar, so are there any chemical peculiarities in Gaia BH3*?
Looking at the light elements, no!
Gaia BH3 is in a halo stream called ED-2. We know that stars that are born together should look similar, so are there any chemical peculiarities in Gaia BH3*?
Looking at the light elements, no!
We derived 29 chemical abundances of this star. This system likely formed from one of the following scenarios:
- Isolated Binary Evolution -- these objects were born together
or
- Dynamical Capture -- these objects were unassociated then became bound later
Chemistry may help solve this!
- Isolated Binary Evolution -- these objects were born together
or
- Dynamical Capture -- these objects were unassociated then became bound later
Chemistry may help solve this!
December 16, 2025 at 7:18 PM
We derived 29 chemical abundances of this star. This system likely formed from one of the following scenarios:
- Isolated Binary Evolution -- these objects were born together
or
- Dynamical Capture -- these objects were unassociated then became bound later
Chemistry may help solve this!
- Isolated Binary Evolution -- these objects were born together
or
- Dynamical Capture -- these objects were unassociated then became bound later
Chemistry may help solve this!
The red giant in this system is metal-poor ([Fe/H] = -2.27), alpha rich, and slightly r-process enhanced.
I obtained ~45 hours of observations on this star using the 2.7m telescope at McDonald Observatory to produce the highest SNR spectrum to date and search for some of the most elusive elements🔭
I obtained ~45 hours of observations on this star using the 2.7m telescope at McDonald Observatory to produce the highest SNR spectrum to date and search for some of the most elusive elements🔭
December 16, 2025 at 7:16 PM
The red giant in this system is metal-poor ([Fe/H] = -2.27), alpha rich, and slightly r-process enhanced.
I obtained ~45 hours of observations on this star using the 2.7m telescope at McDonald Observatory to produce the highest SNR spectrum to date and search for some of the most elusive elements🔭
I obtained ~45 hours of observations on this star using the 2.7m telescope at McDonald Observatory to produce the highest SNR spectrum to date and search for some of the most elusive elements🔭
Idk if this is helpful but it looks like the exact inverse of long term nuclear waste warning message (see message section!): en.wikipedia.org/wiki/Long-te...
Long-term nuclear waste warning messages - Wikipedia
en.wikipedia.org
November 27, 2025 at 1:45 PM
Idk if this is helpful but it looks like the exact inverse of long term nuclear waste warning message (see message section!): en.wikipedia.org/wiki/Long-te...