If super massive black holes (SMBH) were given a job description, it would tell them to park themselves in the middle of a massive galaxy and consume as much gas, dust, and even stars as they could. Like teenage boys in front of a well-stocked fridge, they're happy to oblige. However, even voracious SMBHs have limits, and astronomers have watched as one of them reached its limit.
The study of SMBHs progresses significantly in 2001 when researchers working with data from the ESA's XMM Newton X-ray space telescope. XMM Newton revealed outflows of superheated ionized gas coming from luminous AGN. Now astrophysicists know that these outflows are a characteristic feature of AGN. New research based on XMM Newton observations shows a counterintuitive reverse flow back into an SMBHs vicinity.
The research is "Observing the launch of an Eddington wind in the luminous Seyfert galaxy PG1211+143." It's published in The Monthly Notices of the Royal Astronomical Society, and the authors are Ken Pounds and Kim Page, both from the Department of Physics and Astronomy at the University of Leicester in the UK. Pounds is the lead author of several papers examining PG1211+143.
There's a limit to how much mass an SMBH can accrete. It's called the Eddington limit and it's the theoretical point where outward radiation pressure is balanced with inward gravitational pull. Some objects in some situations can breech this limit and that's called Super-Eddington accretion. During Super-Eddington accretion, SMBHs are expected to create steady-state winds. But this SMBH appears to have reversed its flow, as if there's simply too much gas for it to consume.
Astronomers have been observing PG1211+143 with XMM Newton for 25 years and they've noticed variations in the black hole's outflowing winds. In 2001, the X-ray telescope detected strong outflows moving at 0.15 the speed of light. In 2004 and 2007, Newton detected weaker outflowing winds. In 2015, XMM Newton observed PG1211+143 for five weeks and revealed a complex velocity structure in the winds.
It turns out that PG1211+143 had an inflow that delivered about 10 Earth masses of material back toward the black hole. It gathered in a ring-like structure around the hole. Then, a few days later, there was a powerful new outflow moving at 0.27 the speed of light.
The researchers present a couple of explanations for this strong outflow. The preceding inflow could've disrupted the structure of the corona, the ring of super-heated plasma above the accretion disk. The corona is held together by powerful and complex magnetic fields. The change in accretion flow could've disrupted the magnetic fields holding the corona and allowed the powerful outflow.
Another explanation is based on a newly-detected ring of matter accumulated during the transient inflow. It was detected via gravitational redshift. The outflow is excess matter being ejected from the disk.
The researchers were able to untangle these events by relying on two observatories: the already-mentioned Newton XMM which observes X-rays, and NASA's Neil Gehrels Swift Observatory, which studies gamma-ray bursts but also detects UV. During Super-Eddington accretion, material creates an optically thick disk. The material in the disk is so thick that photons struggle to escape. Swift UV observations showed that the inflow was insufficient to disrupt this disk.
However, XMM Newton found something different. Its X-ray observations showed that additional mass and energy were injected into the disk by the inflow detected in 2014.
This figure shows XMM Newton data in black and Swift data in red. The second black data point is from spacecraft orbit 2659 and shows the transient infalling gas at 0.3 the speed of light. "Both data sets show a deep minimum flux near orbit 2659 (day 16), followed by an increase to a peak near orbit 2664 (day 24)," the authors write. Image Credit: Pounds and Page 2025. MNRAS
The authors preferred explanation concerns the newly-detected ring of matter. "We now propose that the 0.27c wind was launched as a direct result of accretion from that inner ring of matter – at a locally super-Eddington rate – with excess matter then being ejected by radiation pressure," the authors write.
“Establishing the direct causal link between massive, transient inflow and the resulting outflow offers the fascinating prospect of watching a SMBH grow by regular monitoring of the hot, relativistic winds associated with the accretion of new matter,” said lead author Pounds.
This research shows how extraordinarily complex supermassive black holes are. They wield enormous gravitational and magnetic power that shapes their surroundings and affects their galaxies. Transient high-speed winds draw material into the black hole, heat it, and sometimes eject it in high-speed winds.
"The near coincidence of a 0.3c infall velocity detected in revolution 2659, and the wind launch seen 2–3 weeks later, suggest a physical link," the authors write. The discovery of a new ring of matter orbiting the hole and populated by gas from the transient inflow suggest yet another layer of complexity in SMBHs.
