Astro2020 APC White Paper
Studying Black Holes on Horizon Scales with VLBI Ground Arrays
Lindy Blackburn
1
,
2
,
∗
Sheperd Doeleman
1
,
2
,
†
, Jason Dexter
12
, José L. Gómez
16
, Michael D. Johnson
1
,
2
,
Daniel C. Palumbo
1
,
2
, Jonathan Weintroub
1
,
2
, Katherine L. Bouman
1
,
2
,
32
, Andrew A. Chael
1
,
2
,
33
,
34
,
Joseph R. Farah
1
,
2
,
21
, Vincent Fish
4
, Laurent Loinard
18
,
19
, Colin Lonsdale
4
, Gopal Narayanan
28
,
Nimesh A. Patel
2
, Dominic W. Pesce
1
,
2
, Alexander Raymond
1
,
2
, Remo Tilanus
17
,
22
,
23
, Maciek Wielgus
1
,
2
,
Kazunori Akiyama
1
,
3
,
4
,
5
, Geoffrey Bower
6
, Avery Broderick
7
,
8
,
9
, Roger Deane
10
,
11
, Christian M. Fromm
13
,
Charles Gammie
14
,
15
, Roman Gold
13
, Michael Janssen
17
, Tomohisa Kawashima
4
, Thomas Krichbaum
29
,
Daniel P. Marrone
20
, Lynn D. Matthews
4
, Yosuke Mizuno
13
, Luciano Rezzolla
13
, Freek Roelofs
17
,
Eduardo Ros
29
, Tuomas K. Savolainen
29
,
30
,
31
, Feng Yuan
24
,
25
,
26
, Guangyao Zhao
27
1
Black Hole Initiative at Harvard University, 20 Garden Street,
Cambridge, MA 02138, USA
2
Center for Astrophysics
|
Harvard & Smithsonian, 60 Garden
Street, Cambridge, MA 02138, USA
3
National Radio Astronomy Observatory, 520 Edgemont Road,
Charlottesville, VA 22903, USA
4
Massachusetts Institute of Technology, Haystack Observatory,
99 Millstone Road, Westford, MA 01886, USA
5
National Astronomical Observatory of Japan, 2-21-1 Osawa,
Mitaka, Tokyo 181-8588, Japan
6
Institute of Astronomy and Astrophysics, Academia Sinica,
645 N. A’ohoku Place, Hilo, HI 96720, USA
7
Perimeter Institute for Theoretical Physics, 31 Caroline Street
North, Waterloo, ON, N2L 2Y5, Canada
8
Department of Physics and Astronomy, Univ. of Waterloo,
200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
9
Waterloo Centre for Astrophysics, University of Waterloo,
Waterloo, ON N2L 3G1 Canada
10
Department of Physics, University of Pretoria, Lynnwood
Road, Hatfield, Pretoria 0083, South Africa
11
Centre for Radio Astronomy Techniques and Technologies,
Department of Physics and Electronics, Rhodes University, Gra-
hamstown 6140, South Africa
12
Max-Planck-Institut für Extraterrestrische Physik, Giessen-
bachstr. 1, D-85748 Garching, Germany
13
Inst. für Theoretische Physik, Goethe-Universität Frankfurt,
Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany
14
Department of Physics, University of Illinois, 1110 West
Green St, Urbana, IL 61801, USA
15
Department of Astronomy, University of Illinois at Urbana-
Champaign, 1002 West Green Street, Urbana, IL 61801, USA
16
Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la
Astronomía s/n, E-18008 Granada, Spain
17
Department of Astrophysics, Institute for Mathematics, As-
trophysics and Particle Physics (IMAPP), Radboud University,
P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
18
Instituto de Radioastronomía y Astrofísica, Universidad Na-
cional Autónoma de México, Morelia 58089, México
19
Instituto de Astronomía, Universidad Nacional Autónoma de
México, CdMx 04510, México
20
Steward Observatory and Department of Astronomy, Univer-
sity of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
21
University of Massachusetts Boston, 100 William T, Morris-
sey Blvd, Boston, MA 02125, USA
22
Leiden Observatory—Allegro, Leiden University, P.O. Box
9513, 2300 RA Leiden, The Netherlands
23
Netherlands Organisation for Scientific Research (NWO),
Postbus 93138, 2509 AC Den Haag , The Netherlands
24
Shanghai Astronomical Observatory, Chinese Academy of
Sciences, 80 Nandan Road, Shanghai 200030, PRC
25
Key Laboratory for Research in Galaxies and Cosmology,
Chinese Academy of Sciences, Shanghai 200030, PRC
26
School of Astronomy and Space Sciences, Univ. of Chinese
Academy of Sci., No. 19A Yuquan Road, Beijing 100049, PRC
27
Korea Astronomy and Space Science Institute, Daedeok-daero
776, Yuseong-gu, Daejeon 34055, Republic of Korea
28
Department of Astronomy, University of Massachusetts,
01003, Amherst, MA, USA
29
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69,
D-53121 Bonn, Germany
30
Aalto University Department of Electronics and Nanoengi-
neering, PL 15500, FI-00076 Aalto, Finland
31
Aalto University Metsähovi Radio Observatory, Metsähovin-
tie 114, FI-02540 Kylmälä, Finland
32
California Institute of Technology, 1200 East California
Boulevard, Pasadena, CA 91125, USA
33
Princeton Center for Theoretical Science, Jadwin Hall,
Princeton University, Princeton, NJ 08544, USA
34
NASA Hubble Fellowship Program, Einstein Fellow
∗
lblackburn@cfa.harvard.edu,
†
sdoeleman@cfa.harvard.edu
arXiv:1909.01411v2 [astro-ph.IM] 8 Nov 2019
1 Introduction
This white paper outlines a process to design, architect, and implement a global array of
radio dishes that will comprise a virtual Earth-sized telescope capable of making the first
real-time movies of supermassive black holes (SMBH) and their emanating jets. These
movies will resolve the complex structure and dynamics at the event horizon, bringing into
focus not just the persistent strong-field gravity features predicted by general relativity,
but also details of active accretion and relativistic jet launching that drive galaxy evolution
and may even affect large scale structures in the Universe. SMBHs are the most massive
and most compact objects predicted by Einstein’s theory of gravity. They are believed
to energize the luminous centers of active galaxies, where they convert the gravitational
potential energy of infalling matter to radiant power and jetted outflows of charged particles
that can stretch to hundreds of thousands or even millions of light years. We propose to
turn the extreme environment of their event horizons into laboratories where astronomers,
physicists, and mathematicians can actively study the black hole boundary in real-time, and
with a sensitivity and angular resolution that allow them to attack long-standing fundamental
questions from new directions.
Figure
15
as a conservative representation of our
fi
nal M87
imaging results.
The
fi
ducial images from each pipeline
(
Figure
11
)
, as well
as the conservative, blurred, pipeline-averaged images
(
Figure
15
)
provide some evidence for evolution in the ring
structure between April 5, 6 and 10, 11. We discuss this
evolution in more detail in Appendix
E
(
Figure
33
)
. Some
change in the image structure between April 5, 6 and 10, 11 is
necessitated by the variations seen in the underlying closure
phases
(
Paper
III
)
. We
fi
nd more variation in the image pairs
that are separated by larger intervals, suggesting that these
variations are intrinsic. However, we cannot unambiguously
associate the observed variability with coherent evolution of a
speci
fi
c image feature.
Figure
16
shows the visibility amplitude and phase for each
of the three April
11
fi
ducial images as a function of vector
baseline. Note that no restoring beam is required for CLEAN in
this visibility-domain analysis. Each image produces nulls in
the visibility amplitude near the SMA
–
SMT baseline, con-
sistent with the observed amplitudes
(
see Figure
2
)
. The
visibility phase shows rapid swings at these nulls. The
visibilities of the images from the different pipelines are most
similar near the EHT measurements, as expected. On longer
baselines than those sampled by the EHT, the
DIFMAP
image
produces notably higher visibility amplitudes than those of the
eht-imaging
and
SMILI
images, as expected from the fact
that the
DIFMAP
image is fundamentally a collection of point
sources.
7.2. Image Uncertainties
Measuring the variation in images produced in a parameter
survey Top Set allows us to evaluate image uncertainties due to
the explored imaging choices. Figure
17
shows uncertainties
related to imaging assumptions from the largest Top Set
(
that of
the
eht-imaging
parameter survey
)
on April
11 data.
Reconstructed image uncertainties are concentrated in the
regions with enhanced brightness, notably in the three
“
knots
”
in
the lower half of the ring
(
Figure
17
;toppanel
)
. These are also
the regions that show the most variation among different imaging
methods
(
Appendix
I
compares their azimuthal pro
fi
les
)
.
Visibility-domain modeling provides another method to assess
image structure. In Paper
VI
, we explore
fi
tting simple crescent
models to the data. For instance, a crescent with a brightness
gradient and blurring reproduces the north
–
south asymmetry in
images without additional azimuthal structure
(
the
“
blurred and
slashed with LSG
”
crescent of Paper
VI
)
. However, this model
gives
CP
2
c
between 3.2 and 11.5 and
logCA
2
c
between 2.2 and 6.6
for different days and bands when assuming 0% systematic error
(
compare with Table
5
)
. Adding additional degrees of freedom in
the form of three elliptical Gaussian components to the crescent
Figure 14.
Fiducial images of M87 on April
11 from our three separate imaging pipelines after restoring each to an equivalent resolution. The
eht-imaging
and
SMILI
images have been restored with 17.1 and 18.6
μ
as FWHM Gaussian beams, respectively, to match the resolution of the
DIFMAP
reconstruction restored with a
20
μ
as beam.
Figure 15.
Averages of the three
fi
ducial images of M87 for each of the four observed days after restoring each to an equivalent resolution, as in Figure
14
. The
indicated beam is 20
μ
as
(
i.e., that of
DIFMAP
, which is always the largest of the three individual beams
)
.
21
The Astrophysical Journal Letters,
875:L4
(
52pp
)
, 2019 April 10
The EHT Collaboration et al.
Figure 1:
1.3 mm wavelength images of M87 for each of four days during which the source was observed
in 2017 with the Event Horizon Telescope array. All images are restored to an equivalent resolution with a
beam of 20
μ
as. These represent the highest angular resolution images ever made from the surface of the
Earth, and show clearly the predicted photon orbit caused by extreme light bending in the presence of a 6.5
billion solar mass black hole. The central dark region occurs because light rays interior to the photon ring
spiral into the event horizon. There is clear variation in the structure over the span of 5 days.
While ambitious, this vision is grounded in recent remarkable results: on April 10th, 2019,
after a decade of developmental efforts from a global collaboration of scientists [18], the Event
Horizon Telescope (EHT) announced the first successful imaging of a black hole [17], Figure 1.
To accomplish this, the EHT used the technique of very long baseline interferometry (VLBI),
in which radio dishes across the globe are synchronized by GPS timing and referenced to
atomic clocks for stability, thereby synthesizing a single Earth-sized telescope. Through
development of cutting edge instrumentation, the EHT extended the VLBI technique to the
1.3 mm observing band, and by deploying these systems, created a virtual telescope with the
highest angular resolution currently possible from the surface of the Earth. First experiments
[15, 16] confirmed event horizon-scale structures in both Sgr A
∗
and M87. Build-out of the
full EHT enabled detailed imaging of the black hole “shadow” of M87, which is formed by
the lensed photon orbit of the 6.5 billion solar mass black hole at the galaxy’s core. Current
EHT imaging capability is limited by the sparsity of VLBI baseline coverage, and targeted
1
EHT 2017
50
μ
as
0:00
0:05
0:10
0:15
0:20
EHT-II
Truth
0
6
12
18
24
Brightness Temperature (10
9
K)
Truth ngEHT EHT2017
Figure 2:
Reconstructing movies
of flares from Sgr A
∗
with the EHT.
Bottom row: Simulated images of
a “hot spot” orbiting Sgr A
∗
with
a period of
∼
30
minutes (Model
B from [9, 14]). Upper rows:
Corresponding reconstructions of
the model with the EHT2017 and
ngEHT arrays merging 230 and
345 GHz, demonstrating the po-
tential to study the evolution of
flares in Sgr A
∗
on timescales of
minutes [26, 8]. Reconstructions
are performed with visibility am-
plitudes and closure phases, reflect-
ing calibration similar to that of the
EHT2017 data.
expansion of the EHT array by augmenting existing stations, as well as developing new sites,
can greatly increase the scope of EHT core science over the next decade. We refer to the
expanded array as the next-generation EHT, or ngEHT. A separate white paper is dedicated
to a complementary expansion of the EHT array by deployment of a radio telescope in orbit
around the Earth.
2 Key science goals and requirements
The detection of the black hole shadow in M87 [17] has opened up the opportunity for
repeated experimental studies of strong gravity and horizon scale accretion and jet launching
with ngEHT. Future observations will measure the detailed shape and size of the black hole
shadow and surrounding photon ring, allowing direct tests of the Kerr metric describing
black holes in general relativity. An ngEHT will also address fundamental questions about
the role of magnetic fields in the accretion and jet launching process as traced by the observed
time-variable, polarized synchrotron radiation.
2.1 Testing General Relativity
Measuring the shape and size of the shadow and surrounding lensed photon ring provides a
null hypothesis test of General Relativity [24]. The mass and distance of Sgr A
∗
are known
to
∼
1% [21], so the precision of GR tests for this source will be limited primarily by the
fidelity of EHT data and the ability to extract the emission corresponding to the black hole
circular photon orbit and interior shadow. Positional measurements of luminous matter (“hot
spots”) orbiting near the event horizon, as shown in Fig. 2, can be used to map the spacetime
metric near the black hole and constrain the black hole spin. Combining one or more such
EHT measurement of Sgr A
∗
with other observations [e.g., 20] allows a test of the “no hair”
theorem [22, 10, 31].
2
Higher angular resolution allows more precise measurements of the shadow size and shape,
while increased dynamic range improves image fidelity and allows us to extract the thin,
bright photon ring feature from the more diffuse surrounding emission. Snapshot imaging
of Sgr A
∗
on timescales of minutes is required to track relativistic motions around the black
hole.
2.2 The role of magnetic fields in black hole accretion
Magnetic fields play an outsized role in accretion and jet formation. The magnetorotational
instability [MRI, 2] is thought to transport angular momentum and drive accretion onto
the central black hole. Dynamically important magnetic fields can cause instabilities and
flaring on horizon scales [34]. The polarized synchrotron radiation observed by the ngEHT
traces magnetic field geometry (Fig. 3), while its time variability encodes the dynamics of
spiral waves driven by the MRI and magnetic flux eruption events associated with strong
magnetic fields. Triggered multi-wavelength campaigns are needed to fully take advantage of
ngEHT’s capability to spatially resolve structures associated with the energetic, high energy
flares from Sgr A
∗
. The X-ray radiation in Sgr A
∗
flares suggests that particles can be
accelerated to high energy even around a quiescent black hole [13]. Spatially resolving their
radio counterparts will provide new constraints on the acceleration mechanism.
Blurred Sim
ngEHT Image
Figure 3:
Comparison of po-
larization map of a simulation
of M87 [11] blurred to half the
nominal resolution of ngEHT
(left), and a polarimetric re-
construction of synthetic ngEHT
data generated by the simula-
tion (right). ngEHT enables
high fidelity polarimetric re-
constructions, revealing the or-
dered, horizon-scale fields in this
simulation of a “magnetically-
arrested” disk.
Snapshot polarimetric imaging with the future EHT can reveal the structure and dynam-
ics of magnetic fields. Simultaneous polarimetric observations at 230 and 345 GHz will allow
probing the magnetic field degree of ordering, orientation, and strength through Faraday
rotation studies. Spectral index analyses will probe other plasma properties, such as the
electron density and temperature.
2.3 Jet formation
The processes that govern the formation, acceleration and collimation of powerful relativistic
jets in active galactic nuclei (AGN) and X-ray binaries are a half-century-long mystery in
black hole physics. The leading scenarios rely on magnetic fields to extract rotational energy,
either from orbiting material [4] or from the black hole itself [5]. Magnetic fields downstream
further collimate and accelerate the jet to relativistic speeds. EHT observations of M87
3
provide a unique opportunity to study jet launching, collimation, and acceleration at the
base in the immediate vicinity of the black hole.
Figure 4 shows reconstructed 3D GRMHD simulations of the jet launching region in M87
with current and sample ngEHT arrays. The addition of short baselines anchored to existing
large apertures, combined with observations at progressively higher frequencies will improve
both the imaging dynamic range and angular resolution to study formation, collimation and
acceleration of relativistic jets, not only in M87 but also in other nearby AGN [7]. This
opens new possibilities for linking jet power to black hole spin, accretion rate, and disk
magnetization through direct comparison of observation and simulations on scales down to
the event horizon. Triggered observations and centralized data processing will increase the
cadence of the observations, allowing the study of time variable jet ejections first near the
black hole, and subsequently as they emerge from the AGN core.
4
the EHT
-
II reconstructions, which in
clude empirically verified error budgets and estimated performance
of future sites, demonstrates that connecting the horizon
-
scale structure and dynamics near the black hole
to the emergence and launch of the M87 jet is achievable.
Figure 3
:
EHT baseline coverage for
M87 (left) and SgrA*
(right). Each point shows the April 2017 1.3mm
EHT coverage (black), the 1.3mm coverage anticipated for EHT
-
II (black and red), and the a
dded coverage
at 0.87mm (blue).
EHT
-
II images of M87 will open new ave
nues to understand how black holes launch and power
relativistic jets. For instance, if the jet is powered by the spinning black hole, then magnetic fields
threading the horizon are predicted to rotate at approximately half the angular frequency of the bla
ck hole
(e.g., Blandford & Znajek 1977; Macdonald & Thorne 1982). With EHT
-
II observations of M87 over
several weeks, this effect will be directly observable via polarimetric movie reconstructions. In addition,
measurements of the magnetic field strength v
ia Faraday rotation from joint 230+345 GHz observations
will test reveal whether the jet power corresponds to predictions from the Blandford
-
Znajek mechanism.
Figure 4:
Left:
GRMHD snapshot from a simulation of M87 (Chael et al. 2019). Main panel is log
scale;
inset is linear scale.
Middle:
Reconstruction using EHT2017, revealing the circular ~ 40 μas ring surrounding
the black hole shadow but no jet.
Right:
Reconstruction using EHT
-
II, including both 230 and 345 GHz,
revealing both the black hole and its
jet.
ngEHT
Figure 4: GRMHD snapshot from a simulation of M87 (Chael et al. 2019). Main panel is
log scale; inset is linear scale. Middle: Reconstruction using EHT2017, revealing the circular
∼
40
μ
as ring surrounding the black hole shadow but no jet. Right: Reconstruction using
ngEHT, including both 230 and 345 GHz, revealing both the black hole and its jet.
2.4 Objectives and requirements
The quality of ngEHT images/movies and their corresponding traction on key science ques-
tions depend on the baseline coverage of the array as well as overall sensitivity, observing
frequency, bandwidth, and observing/scheduling constraints. Additional improvements in
imaging and analysis algorithms will further drive design requirements and trade-offs in
defining the ngEHT instrument systems and array architecture. We advocate a formal sys-
tem engineering approach, in which key science questions are used to define and select across
technical elements for the array. In Table 1 we outline an abbreviated science traceability
matrix for the ngEHT. The full array design must be explored using system engineering
driven simulation and science optimization process resulting in an expanded STM to define
a phase of ngEHT design, followed by a phase of implementation, both timed to deliver a
functional ngEHT array by the end of the coming decade.
4
STM Shortform for Ground White Paper
Rev 9 July 2019
Science Goals
Measurement Requirements
Developments: Array, Instrument, and Algorithms
Are SMBHs described by
the Kerr metric?
1. Angular resolution of about 10 μas
2. Accelerated baseline sampling to
enable static imaging of SgrA*
1. Enable 345 GHz observations
2. Identify & characterize candidate sites
3. Optimize baseline coverage for Sgr A*
4. Sufficient sensitivity for a fully-connected array
5. Methods to study intra-day variation of Sgr A*
What drives accretion
onto a SMBH and triggers
flaring events?
1. Movies of the Sgr A* accretion flow on
sub-ISCO timescales
2. Polarimetric movies of Sgr A* and
M87 to study magnetic field turbulence &
multi-wavelength flares
3. Coordinated multi-wavelength &
triggered observations
1. Optimize array for rapid baseline sampling
2. Simultaneous 230 & 345 GHz with dual-polarization
3. Methods for polarimetric movie reconstructions
4. Triggered turn-key VLBI scheduling
5. Strategic array redundancy to reduce sensitity to
weather and site loss
What is the role of the
SMBH in forming,
collimating & powering a
relativistic jet?
1. Horizon-scale polarimetric imaging to
measure magnetic field structure
2. Faraday rotation measurements to
measure magnetic field strength
3. Increased image dynamic range from
~10 to ~100 to connect the black hole,
jet & counter-jet
4. Movies of the M87 jet-launching
region over multi-month timescales
1. Co-temporal 230 & 345 GHz with dual-polarization
2. Increased sensitivity through wider bandwidths
3. Optimize baseline coverage for M87 horizon scale
and jet launching region
4. Improved calibration & algorithms for multi-scale and
high dynamic range imaging
5. Enhance array operations to optimize duration,
cadence & quality of observations
Table 1: A short form science traceability matrix (STM). The STM links the key science
questions in the first column with the top level requirements for astronomical measurements
in the second, and these drive the specifications for detailed design, of the array configura-
tion, instrument developments, and software post processing algorithms in the third column.
System engineering will expand this STM in the early phases of an upgrade.
3 Technical elements
Current EHT images are already exceptionally rich scientifically. Following system engi-
neering practices, and referencing the STM in figure 1, we propose to extend the scientific
potential of ground-based mm VLBI observations by quadrupling the current recorded in-
stantaneous bandwidth of the EHT, adding a 345 GHz capability, and incorporating new
sites to the existing array. This last possibility stems from the important realization that
single large apertures in the array (phased ALMA in Chile, the Large Millimeter Telescope
in Mexico, and future phased NOEMA in France) provide such high sensitivity that adding
small-diameter dishes in ideal geographic locations can dramatically improve imaging fidelity
– even for sites where the atmospheric conditions are more variable than is typical for current
mm/submm facilities (Figure 7). By roughly doubling the number of antennas in the EHT
through addition of several new small diameter dishes as well as new stations ngEHT can
reconstruct not just images of extraordinary detail, but movies of the dynamics near the
black hole event horizon.
3.1 New sites and dishes
At the bandwidth projected for the ngEHT, antenna diameters between 6 and 12 m will be
suitably sensitive for new nodes in the array. The Greenland Telescope is an example of a
successful relocation of a 12 m ALMA dish, and a similar dish is being relocated to Kitt Peak
in Arizona. In ngEHT Phase I, designs for new dishes will be explored using approaches that
5
Figure 5: Distribution of stations around the globe. Stations that participated in the
EHT2017 observing campaign are labeled in yellow, while the additional stations that will
be present in the EHT2020 array are labeled in orange. Several possible new site locations
for the ngEHT are labeled in cyan. Current EHT2017 baselines are shown in magenta.
have been successfully used for sub-mm class antennas for the SMA and ALMA [29, 28].
Candidate locations for newly designed dishes will be selected based on weather for sub-
mm observing, existing infrastructure, and improvement to the spatial frequency coverage
of the array [30, 27]. Small dishes are particularly effective close to major ngEHT anchor
sites. An example of an expanded ngEHT array, feasible by 2027, is shown in Figure 5.
Corresponding improvements in the
(
u,v
)
-coverage for the EHT science targets are shown
in Figure 6.
3.2 Receiver and VLBI back end
The EHT presently samples 4 GHz bandwidth in dual polarization and two sidebands for a
total of 16 GHz. This corresponds to 64 Gbps for two-bit recording and Nyquist sampling.
This matches ALMA’s current bandwidth, though efforts are underway to double the ALMA
bandwidth in each sideband over the next decade. The majority of the other EHT sites
already employ receivers with 8 GHz sidebands, and those that do not are typically in the
process of upgrading. A doubling of bandwidth per sideband for the EHT would result in a
record rate of 128 Gbps.
The ability to simultaneously observe the 1.3 mm (230 GHz) and 0.87 mm (345 GHz)
EHT observing bands dramatically improves imaging and movie rendering capability of
the EHT (Figures 2, 4) as well as polarization observations of, for example, Faraday rota-
tion. The ngEHT with 8 GHz per sideband, dual polarization, and simultaneous dual band
230/345 GHz capability requires a recording rate of 256 Gbps. A dual-band EHT receiver
6