🔭 astrophysics

Discovery of Unusual Jet Orientation Variations in the Microquasar GRS 1915+105

Based on three-epoch EAVN observations during 2025 giant radio flares, this paper reports unprecedented large-scale variations in the jet orientation of the microquasar GRS 1915+105, suggesting a warped, precessing inner accretion disk as the underlying cause.

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

Published 2026-06-16

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CC BY 4.0

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

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 a cosmic lighthouse in our own galaxy, a black hole system named GRS 1915+105. For decades, astronomers have watched this object shoot out powerful beams of energy (jets) like a spinning sprinkler. Usually, this sprinkler points in a very steady direction, like a compass needle that never wavers.

However, a team of astronomers using a giant "virtual telescope" made up of radio dishes across East Asia (called the EAVN) recently discovered that this cosmic sprinkler is acting very strangely.

Here is what they found, broken down simply:

1. The "Wobbly" Sprinkler

For most of its history, this black hole's jet has pointed in a Southeast-to-Northwest direction. But in early 2025, the team watched it closely over a period of just 37 days and saw something wild: the jet started spinning.

The Shift: At the start of their observation, the jet was pointing at a sharp angle (118 degrees). Less than a month and a half later, it had swung around to a completely different angle (152 degrees).
The Big Picture: When they looked back at old data, they realized this isn't just a one-time glitch. Since 2023, the jet has been swinging wildly, covering a huge range of angles (from 118 to 188 degrees). It's as if the lighthouse beam is suddenly being spun by a child on a merry-go-round, rather than staying fixed.

2. The "Hidden" Black Hole

Why is this happening now? The paper suggests the black hole is currently "hiding."

The Analogy: Imagine a bright light bulb (the black hole) covered by a thick, swirling fog (a disk of gas and dust).
The Cause: The black hole has been in this "foggy" state since 2018. The scientists think the inner part of this foggy disk is warped and twisting like a wobbly dinner plate that is spinning on a table. Because the jet is launched from the center of this spinning, twisted plate, the jet itself gets pushed around, changing its direction rapidly.

3. The "Exploding" Blob

There was one specific moment during their observations that was particularly weird.

The Shape: Usually, these jets look like thin, straight streams of water. But in one of their snapshots, the jet coming toward us looked like it was spreading out sideways, almost like a blob of jelly expanding as it moves.
The Mystery: This "sideways spreading" has never been seen in this object before. The scientists aren't sure exactly why it happened, but it suggests the material being ejected is behaving very differently than usual, perhaps expanding violently as it shoots out.

4. Why It Matters

This discovery is like finding a new rule of physics in action.

The Connection: The paper links the changing direction of the jet to the twisting of the inner disk. It's like seeing the handle of a spinning top wobble and realizing that the wobble is what's making the top's path curve.
The Future: The scientists say we need to keep watching. Just as you would watch a storm to understand how it moves, they need more observations to confirm if this "twisting disk" theory is the real reason the jet is acting so strangely.

In short: A famous cosmic jet, usually a steady arrow, has suddenly become a spinning, wobbly, and occasionally expanding beam of light, likely because the "engine" launching it is twisting and turning underneath a thick layer of cosmic fog.

Technical Summary: Discovery of Unusual Jet Orientation Variations in the Microquasar GRS 1915+105

Problem Statement
GRS 1915+105, a prototype microquasar in the Milky Way, has historically exhibited a stable radio jet orientation along the southeast–northwest direction with a mean position angle (PA) of $147^\circ \pm 8^\circ$ . However, the source entered a peculiar, persistent X-ray obscured state in 2018, characterized by low X-ray fluxes but episodic radio flares. Recent literature suggests that this obscuration may result from a warped, precessing inner accretion disk. While previous studies noted changes in jet parameters in 2023, the short-term evolution of the jet orientation on day-timescales during this obscured phase remained poorly constrained. This work addresses the need for high-resolution monitoring to characterize the jet's behavior during the current active flaring period in early 2025.

Methodology
The study utilized the East Asia VLBI Network (EAVN) to conduct three-epoch observations of GRS 1915+105 at 6.7 GHz between January 18 and February 24, 2025. These observations were triggered by giant radio flares detected by the RATAN-600 monitoring program.

Observations: Data were recorded in left-hand circular polarization with a 256 MHz bandwidth. The observations employed fast switching between the target and the phase calibrator ICRF J192540.8+122738 (J1925+1227) with a $\sim$ 3-minute cycle.
Data Reduction: Correlation was performed at the Korea–Japan Correlation Center (KJCC). Standard VLBI calibration procedures were applied using AIPS, including a priori amplitude calibration, bandpass calibration, and phase referencing. Notably, due to a system failure at KJCC preventing standard recalculation table delivery, an alternative code developed by N. Sakai was used to generate geodynamical models and delay corrections.
Imaging and Modeling: Phase-referenced images were generated in DIFMAP. The source structure was modeled by fitting circular Gaussian components to the visibility data using the MODELFIT task. Jet orientation (PA) was derived by calculating the best-fit straight line through the relative positions of the jet components and the core, utilizing error-weighted linear regression.

Key Contributions and Results

Discovery of Extreme Jet Orientation Variations: The observations revealed a dramatic shift in the jet's position angle on a timescale of 37 days.
- Epoch A (Jan 18): The jet exhibited the smallest PA ever measured for GRS 1915+105, at $118^\circ \pm 7^\circ$ .
- Epoch B (Jan 25): The PA increased to $131^\circ \pm 6^\circ$ .
- Epoch F (Feb 24): The PA further increased to $152^\circ \pm 2^\circ$ , consistent with the historical mean.
- This represents a variation of $34^\circ$ over 37 days, significantly deviating from the historical mean of $147^\circ \pm 8^\circ$ .
Long-Term Evolution Context: By compiling literature data from 1994 to 2025, the authors demonstrate that the jet orientation remained relatively stable until 2015. However, since 2023, the jet has exhibited significant variations, ranging from $118^\circ$ to $188^\circ$ . The 2025 observations capture the extreme lower bound of this new variability regime.
Peculiar Morphology in Epoch F: The image from Epoch F revealed an unusual structure where the bright approaching jet component (F1) showed a northeastward extension relative to its intensity peak.
- Verification: Extensive tests confirmed this feature is real and not an imaging artifact, including self-calibration with reduced solution intervals, splitting data into temporal halves, and sequential antenna removal.
- Flux Ratio: The jet-to-counterjet flux density ratio ( $R_S$ ) in Epoch F was calculated to be $12.3 \pm 3.4$ , significantly higher than values observed in previous epochs ( $<10$ ) and suggesting highly asymmetric ejections.
- Interpretation: The authors suggest this morphology indicates lateral spreading of the approaching jet blob, a phenomenon not previously reported in this source.

Significance and Claims
The paper claims that the observed rapid and large-scale variations in jet orientation, occurring during the source's persistent X-ray obscured state, provide strong evidence for a dynamic inner accretion disk.

Precession Hypothesis: Drawing parallels to the black hole binary V404 Cygni, the authors propose that the jet orientation changes arise from the precession of a warped, inner slim accretion disk. This precession is likely driven by spin–orbit misalignment.
Consistency with X-ray Data: This interpretation aligns with recent X-ray spectroscopic studies (e.g., J. M. Miller et al. 2025) which suggest a warped, precessing inner disk is responsible for the observed X-ray obscuration and emission lines.
Unusual Ejection: The detection of lateral spreading in the approaching jet component suggests complex hydrodynamics in the ejection process, potentially linked to the same precessing disk mechanism.

The authors conclude that while the jet orientation has stabilized historically, the current epoch (post-2023) represents a distinct phase of instability. Future multi-wavelength observations are identified as essential to confirm the disk-jet precession scenario and investigate the origin of the peculiar lateral spreading.

1. The "Wobbly" Sprinkler

2. The "Hidden" Black Hole

3. The "Exploding" Blob

4. Why It Matters

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