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Distinct Jet Properties in the X-Ray-Obscured State of GRS 1915+105

Observations of GRS 1915+105 during its current X-ray-obscured state reveal distinct jet morphologies and significantly slower propagation speeds compared to its previous unobscured phase, supporting the paradigm that jet properties fundamentally differ between these two states.

Original authors: Xi Yan, Lang Cui, Sergei Trushkin, Shuangjing Xu, Wu Jiang, Zhen Yan, Sándor Frey, Timur Mufakharov, Ruchika Dhaka

Published 2026-07-31

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CC BY 4.0

Original authors: Xi Yan, Lang Cui, Sergei Trushkin, Shuangjing Xu, Wu Jiang, Zhen Yan, Sándor Frey, Timur Mufakharov, Ruchika Dhaka

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe as a cosmic dance floor where stars and black holes spin in a wild, high-energy tango. In this dance, a special kind of partner called an "X-ray binary" often forms: a hungry black hole and a companion star locked in a tight embrace. As the black hole pulls gas from its partner, it doesn't just swallow it; it often shoots out two powerful beams of energy, like twin water hoses spraying from a garden sprinkler. These are called "jets." For decades, astronomers have watched one specific cosmic dancer, a system named GRS 1915+105, and they were amazed. Before 2019, this system was shooting out jets that seemed to move faster than light (a trick of perspective called "superluminal motion"), zooming away at incredible speeds. But then, something strange happened. The system seemed to get "foggy" or "obscured," as if a thick blanket of gas had wrapped around the black hole, hiding the central action from our X-ray telescopes. The big question for scientists became: When the black hole is hidden behind this cosmic fog, does it still shoot out those same super-fast jets, or does the fog change the dance entirely?

This paper is like a detective story where astronomers used a giant, planet-sized camera to peek through that fog. The team, led by researchers from China, Russia, and Korea, watched GRS 1915+105 in 2025, right when it was having some massive radio flares. They used a network of radio telescopes across East Asia (the EAVN) to take incredibly sharp pictures of the jets, zooming in to see details as small as a few billion miles across. They compared two different moments in time. In the first snapshot, they saw a bright center with a long, stretched-out jet, looking a bit like a classic firehose. But in the second snapshot, taken just a week later, the center was dark and invisible, and instead, they saw two bright, symmetrical blobs floating apart, looking more like two glowing marbles drifting in space.

The most surprising discovery came when they tried to catch these blobs in motion. If the jets were still the super-fast, relativistic ones they used to be, the blobs should have zoomed across the sky noticeably during the five hours they were watching. It's like if you watched a race car for five minutes and expected to see it cross the finish line, but instead, it barely moved. The astronomers found that the jets didn't budge significantly. By doing some math based on how far apart the blobs were and how they looked, they calculated that these new jets are moving at a speed of about 0.40 times the speed of light (or less). This is much slower than the "super-fast" jets (which were moving at least as fast as light) seen before 2019.

The paper suggests that the "foggy" state of the black hole is the reason for this change. It seems that when the black hole is obscured, it launches jets that are not only slower but also wobbly and changing direction, unlike the steady, high-speed beams of the past. The authors propose that the thick gas surrounding the black hole might be acting like a heavy weight, slowing the jets down as they try to push through, or perhaps the disk of gas feeding the black hole is tilting and spinning in a way that makes the jets wobble. While they can't say for sure exactly why this is happening yet, the evidence strongly points to a new rule: black holes in the "obscured" state behave very differently from those in the clear state. It's a reminder that even in the extreme environment of a black hole, the conditions around it can completely change the rules of the game.

Technical Summary: Distinct Jet Properties in the X-Ray-Obscured State of GRS 1915+105

Problem Statement
GRS 1915+105, the archetypal Galactic black hole X-ray binary (XRB) known for its relativistic superluminal jets, transitioned from a long-lasting unobscured state to an X-ray-obscured state in 2019. This obscured state is characterized by high hydrogen column densities ( $N_H \sim 10^{22}–10^{24}$ cm $^{-2}$ ), which prevent direct observation of the central accretion flow. While the source continues to exhibit episodic radio flares, the kinematic properties of the jets launched during this obscured phase remain poorly understood compared to the well-studied pre-2019 relativistic jets. Recent theoretical work by Fender & Motta (2025, 2026) proposes a new paradigm suggesting that jets in obscured systems are inherently slower and prone to precession, contrasting with the fast, stable jets in unobscured systems. This study aims to test this paradigm by analyzing the physical properties of jets observed in 2025 during the obscured state.

Methodology
The authors utilized East Asia VLBI Network (EAVN) observations at 6.7 GHz conducted during two distinct epochs (A and B) in early 2025, coinciding with strong radio flares detected by the RATAN-600 radio telescope.

Data Analysis: VLBI flux densities were extracted from calibrated visibility data using the AIPS package with 10-second time bins to monitor hour-scale variability.
Imaging: The source structure was modeled using circular Gaussian components via the DIFMAP package. Epoch A was observed three days after Flare I (evolving from optically thick to thin), while Epoch B coincided with the peak of Flare II (optically thin).
Kinematic Constraints: Apparent proper motions were derived by fitting linear functions to the radial separation of jet components relative to the core over 5-hour intervals. Intrinsic jet speeds ( $\beta$ ) and viewing angles ( $\theta$ ) were constrained using two independent methods: (1) the angular separation asymmetry between approaching and receding components, and (2) the brightness ratio of the twin jets combined with the spectral index.
Comparative Analysis: The derived parameters for the 2025 obscured jets were compared against historical data from the pre-2019 unobscured state, utilizing a source distance of $9.4 \pm 1.0$ kpc.

Key Results

Contrasting Jet Morphologies:
- Epoch A: Revealed a bright radio core accompanied by extended, two-sided jet emission. The jet orientation was measured at a position angle (PA) of $118^\circ \pm 7^\circ$ .
- Epoch B: Showed no detectable radio core. The structure was dominated by two bright, symmetric, well-separated jet blobs (SE2 and NW2) with a PA of $131^\circ \pm 6^\circ$ .
Lack of Detectable Motion: Despite 5-hour observations, no significant jet motion was detected in either epoch. The upper limit on apparent proper motion was constrained to $\lesssim 0.3$ mas h $^{-1}$ . If the jets possessed the superluminal speeds typical of the pre-2019 era, a displacement of $\sim 5$ mas would have been expected and detectable; the absence of such motion indicates significantly slower propagation.
Intrinsic Jet Speed: Based on the symmetry of the jet components in Epoch B and the non-detection of motion, the authors derived a constraint of $\beta \cos \theta \approx 0.11$ . Combined with the upper limit on apparent speed, this yields an intrinsic jet speed of $\beta \Gamma \lesssim 0.40$ . This is substantially lower than the $\beta \Gamma \gtrsim 1$ values characteristic of pre-2019 jets.
Orientation Variability: The jet orientations observed in 2025 ( $118^\circ$ and $131^\circ$ ) differ from the historical mean PA of $147^\circ \pm 8^\circ$ and align with recent findings of large orientation variations ( $118^\circ$ – $188^\circ$ ) since 2023, suggesting jet precession.

Significance and Claims
The paper claims that these findings provide robust observational support for the emerging paradigm proposed by Fender & Motta (2025, 2026). Specifically, the results demonstrate that jets launched by GRS 1915+105 during its X-ray-obscured state exhibit distinct propagation properties compared to its unobscured state: they are significantly slower ( $\beta \Gamma \lesssim 0.40$ vs. $\beta \Gamma \gtrsim 1$ ) and display large variations in orientation, likely indicative of precession.

The authors suggest that these distinct properties may arise from a denser environment and higher accretion rates in the obscured state, potentially causing rapid mass loading and deceleration of the jets shortly after launch. They also note that the observed orientation changes could be explained by a warped, precessing accretion disk. The study concludes that the post-2019 jets of GRS 1915+105 are fundamentally different from the relativistic outflows observed prior to 2019, reinforcing the link between accretion state and jet physics in X-ray binaries.

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