EI2GYB > ASTRO 19.11.25 12:45l 52 Lines 6159 Bytes #200 (0) @ WW
BID : 47730_EI2GYB
Read: GUEST
Subj: How three runaway stars solved a galactic mystery
Path: ED1ZAC<ED1ZAC<LU4ECL<K1AJD<GB7BED<EI2GYB
Sent: 251119/1330Z 47730@EI2GYB.DGL.IRL.EURO LinBPQ6.0.25
_ _
(_\ /_)
)) ((
.-"""""""-.
_ _ _ _ /^\/ _. _. \/^\
/ \ ___| |_ _ __ ___ | \ | | _____ _____ \( /__\ /__\ )/
/ _ \ / __| __| '__/ _ \ | \| |/ _ \ \ /\ / / __| \, \o_/_\o_/ ,/
/ ___ \\__ \ |_| | | (_) | | |\ | __/\ V V /\__ \ \ (_) /
/_/ \_\___/\__|_| \___/ |_| \_|\___| \_/\_/ |___/ `-.'==='.-'
__) - (__
+------------------------------------------------------------------------------+
How three runaway stars solved a galactic mystery
All motion is relative. That simple fact makes tracking the motion of distant objects outside our galaxy particularly challenging. For example, there has been a debate among astronomers for decades about the path that one of our nearest neighbors, the Large Magellanic Cloud (LMC), took over the last few billion years. A new paper posted to the arXiv preprint server by Scott Lucchini and Jiwon Jesse Han from the Harvard Center for Astrophysics grapples with that question by using a unique technique-the paths of hypervelocity stars.
So what is a "hypervelocity star"? When a binary star system moves too close to a supermassive black hole, the tidal forces from the black hole disrupt the binary. Typically this results in one star that is captured into orbit around the black hole, which the other loses its gravitational bond to its partner, and the resulting force slings it out of the system at speeds greater than 1,000 km/s. Eventually, stars traveling that quickly will leave the galaxy they are bound to entirely, and standing in isolation is the gulf between galaxies.
Tracking these hypervelocity stars on their trajectory can provide a line back to where they were originally cast out of their binary system. The authors combed through Gaia's Data Release 3 (DR3) and found three stars that they think were ejected from the LMC. One, known as Hyper Velocity Star (HVS) 3 has long been thought to come from the LMC. But the two other candidates (HVS 7 and HVS 15) were only recently discovered with trajectories that make it clear they didn't come from the Milky Way-making the LMC their most likely source.
Tracing where those stars were ejected from could point to the location of the supermassive black hole that sent them on their way. There has even been debate about whether the LMC has a supermassive black hole in its center at all. While the existence of HVSs from the LMC provides more proof that there likely is, it still isn't a clear-cut direct observation. So finding where the SMBH is, and therefore where to look for that direct observation, is one key result of the paper.
But it's not as easy as drawing a straight line from the HVS's current position back to their origin. Plenty of things get in the way of the motion of these galaxies-not the least of which is dark matter. To account for this, the authors ran simulations of both the Milky Way's and LMC's motion, and included a component of "dynamical friction" that represented the drag the galaxies experienced when moving through a field of smaller particles.
With those models, the authors were able to constrain the "corridor" the LMC had moved through over the last few million years by 50%. However, they weren't able to answer a fundamental question about the LMC itself-whether it's on its first or second pass of our galaxy. While we believe the LMC is gravitationally bound to the Milky Way, models show that it could either be on its first orbit of us, or it could have completed its first orbit somewhere on the order of 6-8 billion years ago, and is currently making its way through its second.
The new dynamical friction model and corridor fit with models of both First Passage and Second Passage models, though both used very different components in their own models. Further discussion in the paper hints that the Second Passage model might not be sufficiently robust to truly reflect the complexities of these galactic-level orbital mechanics.
There was another important question that the authors believe they have now answered-where to look for the LMC's SMBH. They provide exact coordinates, and note that it is actually offset by about 1.5 degrees from the visual center of the LMC. That offset appears to be due to the chaotic tidal forces introduced by another of our closest companions-the Small Magellanic Cloud (SMC).
Further study is needed, though, as the paper is reliant on only three stars for its conclusions. The data for those three stars isn't even that well constrained either. With some observational time to resolve their proper motions, even further constraints on the path the LMC has taken, as well as on how dark matter interacts with the movement of galaxies, would be possible. Now someone will just have to get some time on one of the Great Observatories to take a look. That might be a tall ask, but someday we'll be able to truly pinpoint the dark heart of our nearest galactic neighbor.
+------------------------------------------------------------------------------+
================================================================================
= ____ __ ____ ___ _ _ ____ ____ ____ ____ =
= ( __)( )(___ \ / __)( \/ )( _ \ ( _ \( _ \/ ___) =
= ) _) )( / __/( (_ \ ) / ) _ ( ) _ ( ) _ (\___ \ =
= (____)(__)(____) \___/(__/ (____/ (____/(____/(____/ =
= Serving The Irish Packet Radio Network Since 2006 =
= Packet: EI2GYB@EI2GYB.DGL.IRL.EURO / EI2GYB@WINLINK.ORG =
= Email/PayPal: EI2GYB@GMAIL.COM =
================================================================================
Read previous mail | Read next mail